🔶  Abundant

$n$ is an abundant number if $σ(n) > 2n$. An abundant number is a number for which the sum of its proper divisors is greater than the number itself.

  • isAbundant, is005101, I005101, F005101, L005101, V005101.

🔶  AltPartitions

Two alternative implementations of integer partitions. The first one implements the 'visit-pattern' in Fortran style. Compared to the implementation in JuliaMath/Combinatorics:

For n = 50 the benchmark shows:

  • 0.141849 seconds ( 9 allocations: 1.672 KiB) [NEXPAR]
  • 0.111040 seconds (408.45 k allocations: 40.882 MiB, 21.10% gc time) [JuliaMath]

For n = 100 the benchmark shows:

  • 167.598273 seconds ( 15 allocations: 4.813 KiB) [NEXPAR]
  • 86.960344 seconds (381.14 M allocations: 48.735 GiB, 11.29% gc time) [JuliaMath]

Our function is slower but the Combinatorics function takes vastly more space.

In the second alternative implementation the representation of the partitions for fixed n is a weakly increasing lists ordered lexicographicaly. It has a nice algorithm implemented directly (i.e. without iteration).

  • Partition, V080577, V026791

🔶  AndreNumbers

Generalized André numbers count the $m$-alternating permutations of length $n$, cf. A181937.

[  SEQ  ] n|k [0][1][2][3][4] [5] [6]  [7]   [8]   [9]  [10]
[V000012] [1]  1, 1, 1, 1, 1,  1,  1,   1,    1,    1,     1
[V000111] [2]  1, 1, 1, 2, 5, 16, 61, 272, 1385, 7936, 50521
[V178963] [3]  1, 1, 1, 1, 3,  9, 19,  99,  477, 1513, 11259
[V178964] [4]  1, 1, 1, 1, 1,  4, 14,  34,   69,  496,  2896
[V181936] [5]  1, 1, 1, 1, 1,  1,  5,  20,   55,  125,   251
[V250283] [6]  1, 1, 1, 1, 1,  1,  1,   6,   27,   83,   209
  • André, C000111, V000111, V178963, V178964, V181936, V250283.

🔶  BellNumbers

The Bell transform transforms an integer sequence into an integer triangle; also known as incomplete Bell polynomials. Let $X$ be an integer sequence, then

$B_{n, k}(X) = \sum_{m=1}^{n-k+1} \binomial{n-1}{m-1} X[m] B_{n-m,k-1}(X)$

where $B_{0,0} = 1, B_{n,0} = 0$ for $n≥1, B_{0,k} = 0$ for $k≥1$.

The Bell transform is (0,0)-based and the associated triangle always has as first column 1,0,0,0,... This column is often missing in the OEIS. Other Stirling number related sequences are implemented in the module StirlingLahNumbers.

  • BellTrans, BellTriangle, BellNumberList, BellNumber
  • V000110, L000110, T137452, T264428, T137513, T104556, T001497, T132062, T039683, T203412, T004747, T051141, T265606, T119274, T000369, T051142

🔶  BernoulliNumbers

We are primarily concerned with the integer Bernoulli numbers.

Cf. $A000182 (m=2), A293951 (m=3), A273352 (m=4), A318258 (m=5).$

[1] [0, 1,    0,       0,             0,                  0]
[2] [0, 1,   -2,      16,          -272,               7936]
[3] [0, 1,   -9,     477,        -74601,           25740261]
[4] [0, 1,  -34,   11056,     -14873104,        56814228736]
[5] [0, 1, -125,  249250,   -2886735625,    122209131374375]
[6] [0, 1, -461, 5699149, -574688719793, 272692888959243481]

The rational Bernoulli numbers are defined here with $B(1) = 1/2$. Why this is preferred over $B(1) = -1/2$ is explained in the Bernoulli Manifesto.

  • BernoulliInt, BernoulliIntList, Bernoulli, BernoulliList
  • V195441, V065619, V281586, V281588, V027641, L065619

🔶  BinaryInteger

For positive n, BinaryIntegerLength is $⌊ \log_{2}(n) ⌋ + 1$, BinaryIntegerLength(0) = 0.

  • BinaryIntegerLength, Bil, V001855, V003314, V033156, V054248, V061168, V083652, V097383, V123753, V295513

🔶  BinaryQF

A binary quadratic form over Z is a quadratic homogeneous polynomial in two variables with integer coefficients, $q(x, y) = ax^2 + bxy + cy^2$.

A quadratic form $q(x, y)$ represents an integer $n$ if there exist integers $x$ and $y$ with $q(x, y) = n$. We say that $q$ primitively represents $n$ if there exist relatively prime integers $x$ and $y$ such that $q(x, y) = n$.

Ported from BinaryQuadraticForms where you can find much more information on this subject.

  • L002476, L008784, L031363, L034017, L035251, L038872, L038873, L042965, L057126, L057127, L068228, L084916, L089270, L141158, L242660, L243655, L244779, L244780, L244819, L243168, L244291, L007522

🔶  BooleanOperations

The 16 boolean operations

  • FALSE, AND, DIF, PRJ1, CNIMP, PRJ2, XOR, OR, NOR, EQV, NEG2, CIMP, NEG1, IMP, NAND, TRUE

evaluated bitwise on the binary expansions of integers.

The main function is

  • Bits(op::String, n::Int, k::Int, algo=max)

where op are the above acronyms. If the lengths of the binary expansions of $n$ and $k$ are different, the parameter 'algo=min' offers the choice to reduce the range of comparison to the smaller range or to the larger range, 'algo=max', which will first pad the representation of the smaller operand with 0's up to the length of the larger operand.

  • Not, And, Dif, Cnimp, Xor, Or, Nor, Eqv, Cimp, Imp, Nand, BinDigits, BoolOps, Bits, V035327, V003817, V129760, V142151, V080079, V086799, V038712, V163617, V006257, V048724, V003188, V038554, V048735, V213370, V080940, V135521, , V280172.

🔶  CantorMachines

Cantor's enumeration of N X N revisited.

  • Cantor-Machine, Cantor-Enumeration, Cantor-Pairing, Cantor-BoustrophedonicMachine, Cantor-BoustrophedonicEnumeration, Cantor-BoustrophedonicPairing, RosenbergStrong-BoustrophedonicMachine, RosenbergStrong-BoustrophedonicEnumeration, RosenbergStrong-BoustrophedonicPairing

🔶  CarmichaelNumbers

  • isCarmichael, I002997, F002997, L002997
  • isweakCarmichael, I225498, F225498, L225498

🔶  ClausenNumbers

  • ClausenNumber, ClausenNumberList, V002445, L002445, V027642

🔶  CombinationsIterator

  • Combinations

🔶  Compositions

  • T097805, L097805, V097805, M097805

🔶  Counts

  • PreviousPrime, NextPrime, PrimePiList, takeFirst, Nth, Count, List, HilbertHotel
  • L000961, L002808, L005117, L013928, L025528, L065515, L065855, L069637, L246547, L246655, L000720, V007917, V151800, V257993

🔶  CyclotomicBinaryForms

E. Fouvry, C. Levesque, M. Waldschmidt, Representation of integers by cyclotomic binary forms, arXiv:1712.09019 [math.NT], 2017.

  • is206864, F206864, I206864, L206864, is206942, F206942, I206942, L206942, is293654, F293654, I293654, L293654, is296095, F296095, I296095, L296095, V299214, L299214, is299498, F299498, I299498, L299498, is299733, L299733, is299928, F299928, I299928, L299928, is299929, F299929, I299929, L299929, is299930, F299930, I299930, L299930, is325143, F325143, I325143, L325143, is325145, F325145, I325145, L325145

🔶  DedekindEta

  • DedekindEtaPowers, RamanujanTau, RamanujanTauList, PartitionNumberList

🔶  DelehamDelta

Philippe Deléham’s Δ-operation maps, similar to the Riordan product, two integer sequences on a lower triangular matrix. It effectively computes a continued fraction depending on the two input sequences!

Applying Deléham's Δ-operation often gives an additional first column or an additional main diagonal in the resulting triangle compared to what is listed in the OEIS.

Introduction to the Riordan Square

  • DeléhamΔ, T084938, T060693, T106566, T094665, T090238, T225478, T055883, T184962, T088969, T090981, T011117

🔶  EulerTransforms

  • V006171, L006171, V107895, L107895, V061256, L061256, V190905, L190905, V275585, L275585, V290351, L290351

🔶  Fibonacci

  • I000045, F000045, L000045, V000045, R000045, is000045

🔶  FigurativeNumbers

  • PolygonalNumber, PyramidalNumber, V014107, V095794, V067998, V080956, V001477, V000217, V000290, V000326, V000384, V000566, V000567, V001106, V001107, V005564, V058373, V254749, V000292, V000330, V002411, V002412, V002413, V002414, V007584, V007585

🔶  GaussFactorials

The Gauß factorial is $∏_{1 ≤ j ≤ N, j ⊥ n} j$, the product of the positive integers which are $≤ N$ and are prime to $n$.

  • GaussFactorial, I193338, F193338, L193338, V193338, I193339, F193339, L193339, V193339, V216919, V001783, V055634, V232980, V232981, V232982, V124441, V124442, V066570

🔶  GeneralizedBinomial

P. Luschny, Generalized Binomial, OEIS Wiki.

  • Binomial, Pascal, T007318

🔶  GeneralizedFibonacci

  • The classical Fibonacci numbers are exported from the module Fibonacci. See I000045, F000045, L000045, V000045, R000045 and is000045.
  • Fibonacci(n) is defined as the number of compositions of n with no part equal to 1. They are the special case Fibonacci(n) = Multinacci(2, n).
[m\n] 0  1  2   3   4   5    6    7     8     9    10    11
----------------------------------------------------------------
[0]   1, 0, 0,  0,  0,  0,   0,   0,    0,    0,    0,    0, ...
[1]   1, 1, 1,  1,  1,  1,   1,   1,    1,    1,    1,    1, ...
[2]   1, 1, 2,  3,  5,  8,  13,  21,   34,   55,   89,  144, ...
[3]   1, 1, 3,  4,  9, 14,  28,  47,   89,  155,  286,  507, ...
[4]   1, 1, 4,  5, 14, 20,  48,  75,  165,  274,  571,  988, ...
[5]   1, 1, 5,  6, 20, 27,  75, 110,  275,  429, 1001, 1637, ...
[6]   1, 1, 6,  7, 27, 35, 110, 154,  429,  637, 1638, 2548, ...
  • Multinacci, V309896, V006053, V188021, V231181

🔶  HighlyAbundant

  • I002093, F002093, L002093, V002093, I034885, F034885, L034885, V034885

🔶  Hyper1F1

GammaHyp: $(a, b, c, d)$$Γ(a)$ Hypergeometric$1F1(b, c, d).$

  • GammaHyp, V000255, V000262, V001339, V007060, V033815, V099022, V251568

🔶  IntPartitions

All integer partitions are listed by two orderings: IntegerPartitions(n, byNumPart) IntegerPartitions(n, byMaxPart)

Or restricted to partitions of length m: IntegerPartitions(n, m)

The partition coefficients, which are the multinomial coefficients applied to partitions, are given in both orderings (L036038, L078760).

The partition numbers and the number of partitions of n into k parts are given as PartitionNumber(n) and PartitionNumber(n, k), (V000041, L072233).

The sum of all partition coefficients of n is efficiently computed with L005651.

  • V000041, V088887, I072233, L072233, L036038, L078760, L005651, L262071, L292222, L115621, L328917

🔶  JacobiTheta

The $q$-expansion of the Jacobi theta functions 3 and 4 raised to the power $r$ is computed for various values of $r$.

  • JacobiTheta3Powers, JacobiTheta4Powers, L000122, L002448, L004018, L104794, L005875, L213384, L000118, L035016, L008452, L096727, L000132, L000141, L008451, L000143, L000144, L008453, L000145, L276285, L276286, L276287, L004402, L004406, L004407, L015128, L004403, L001934, L004404, L004405, L004408, L004409, L004410, L004411, L004412, L004413, L004414, L004420, L004421, L004415, L004416, L004417, L004418, L004419, L004422, L004423, L004424, L004425

🔶  Kolakoski

  • KolakoskiList, C000002, I000002, L000002

🔶  LahNumbers

  • Posets: Partially ordered sets (posets) on n elements that consist entirely of k chains (nonempty, linearly ordered subsets).
  • Set partitions: Number of ways to split {1,..,n} into an ordered collection of n+1-k nonempty sets that are noncrossing).
  • Dyck paths: Dyck n-paths with n+1-k peaks labeled 1,2,..n+1-k in some order.

See Lah numbers

  • Lah, LahTriangle

🔶  LandauConstants

  • V277233(n) / 4^V005187(n) are the Landau constants. These constants are defined as G(n)$= ∑_{j=0..n} g(j)^2$ with the normalized central binomial
g(n) = (2n)! / (2^n n!)^2 = V001790(n) / V046161(n).
  • V327495(n) / 4^V327492(n) are the rationals considered here. These numbers are defined as H(n)$= ∑_{j=0..n} h(j)^2$ with the normalized swinging factorial
h(n) = n! / (2^n ⌊n/2⌋!)^2 = V163590(n) / V327493(n).
  • In particular, this means that we have the pure integer representations
V277233(n) = ∑{k=0..n}(V001790(k) 2^{V005187(n) - V005187(k)})^2;
V327495(n) = ∑{k=0..n}(V163590(k) 2^{V327492(n) - V327492(k)})^2.
  • V000120, V102376, V011371, V120738, V060818, V124399, V056982, V001511, V046161, V001316, V163590, V327492, V005187, V001790, V277233, V327495, V327493, V327491, V007814, V001803, V327494, V006519, V000265, Bin, BitCount, EvenPart, OddPart

🔶  NarayanaCows

  • NarayanasCows, L214551

For background information see

🔶  NodesAndEdges

Rooted trees and similar topics.

  • V000055, V000081, V000106, V209397, V217420, V095350, V002494, V055542, V055543, V055544, V000088, L087803, L036039

🔶  NumberTheory

  • τ, σ, σ2, ϕ, ω, Ω, ⊥, ⍊
  • Divisors, PrimeDivisors, Factors, Radical, mods, Divides, isPrime, isCyclic, isStrongCyclic, isOdd, PrimeList, isPrimeTo, isStrongPrimeTo, isNonnegative, isPositive, isEven, isSquare, isComposite, isSquareFree, isPrimePower, isPowerOfPrimes, isPerfectPower
  • V000005, V000010, V000203, V001222, V001221, V008683, V181830, V034444, I003277, L003277, V061142, V034386, V002110, I050384, L050384, V001157

🔶  OEISUtils

A collection of utilities for handling OEIS related tasks.

🔶  OrthoPolynomials

  • OrthoPoly, InvOrthoPoly, T053121, T216916, T217537, T064189, T202327, T111062, T099174, T066325, T049310, T137338, T104562, T037027, T049218, T159834, T137286, T053120, T053117, T111593, T059419, L217924, L005773, L108624, L005425, L000085, L001464, L003723, L006229

🔶  Polynomials

Mostly convenient functions to deal with polynomials as often used in connection with ordinary and exponential generating functions. The naming scheme used is roughly described by:

Poly       <-> Coeffs
AltPoly    <-> Poly(AltCoeffs)
EgfPoly    <-> Poly(EgfCoeffs)
OgfPoly    <-> Poly(OgfCoeffs)
AltEgfPoly <-> Poly(AltEgfCoeffs)

Here 'Alt' stands for alternating, 'Egf' for exponential generating function, 'Ogf' for ordinary generating function.

  • Coeffs, CoeffSum, CoeffAltSum, CoeffConst, CoeffLeading, AltCoeffs, Diagonal, Central, EgfCoeffs, AltEgfCoeffs, Poly, AltPoly, EgfPoly, AltEgfPoly, ReflectPoly.

🔶  PrimesIterator

  • Primes, PrimePi, PrimeSieve

🔶  PrimeSwingFactorial

Cf. P. Luschny, Swing, divide and conquer the factorial, excerpt.

  • PSfactorial, Swing

🔶  Products

  • ∏, Product, F!, RisingFactorial, ↑, FallingFactorial, ↓, MultiFactorial
  • V000407, V124320, V265609, V000142, V081125, V001147, V000165, V032031, V007559, V008544, V007696, V001813, V008545, V047053

🔶  QueensProblems

For some background see: Backtracking with profiles.

  • Queens, L319284

🔶  RationalTrees

Rational trees as understood here are binary trees enumerating the positive or nonnegative rational numbers. Examples are the Euclid tree, the Kepler tree and the Stern-Brocot tree (a.k.a. Farey tree). They are closely related to binary partitions and to Stern's diatomic sequence or Dijkstra's fusc function.

Malter, Schleicher, Zagier, New looks at old number theory, Amer. Math. Monthly, 120(3), 2013, pp. 243-264.

  • EuclidTree, CalkinWilfTree, SchinzelSierpinskiEncoding

🔶  RecordSearch

The type object to construct an iterated search for records in sequences.

  • Records

🔶  RiordanSquares

The Riordan product is a map a, b ↦ [a, b] associating two formal power series a, b with a lower triangular matrix [a, b]. The Riordan square is the case a = b of the Riordan product. Formally we can describe the Riordan square as a transform RS: Z[[x]] ↦ Mat[Z] which maps power series over the integers to (lower triangular) integer matrices.

  • RiordanProduct, RiordanSquare
  • T039599, T116392, T172094, T321620, T321621, T321623, T321624, T322942

Introduction to the Riordan Square

🔶  SelfConvolutive

Some exactly solvable self-convolutive recurrences.

  • SelfConvRec, L000698, L001710, L003319, L005411, L005412, L006012, L006318, L047891, L062980, L082298, L082301, L082302, L105523, L107716, L111529, L111530, L111531, L111532, L111533, L146559, L167872

🔶  SeqTests

Alias for isoeisinstalled.

🔶  SeqUtils

Nemo is a library designed, developed and maintained by William Hart with the help of others. Many functions in our project are based on Nemo.

🔶  SeriesExpansion

The generating functions of various combinatorial and number-theoretic functions.

  • Coefficients, EgfExpansion, G000045, G000257, L000257, G000032, L000032, G000073, L000073, G000108, L000108, G000957, L000957, G001003, L001003, G001006, L001006, G001045, L001045, G002426, L002426, G005043, L005043, G006318, G068875, L068875

🔶  SetPartitions

  • SetPartitions(s::AbstractVector)

Return an iterator over all set partitions of the elements of the array $s$, represented as arrays of arrays.

  • SetPartitions(n::Int)

Return an iterator over all set partitions of the elements of the array $[1,2,...,n]$, represented as arrays of arrays.

  • SetPartitions(s::AbstractVector, m::Int)

Return all set partitions of the elements of the array $s$ into exactly $m$ subsets, represented as arrays of arrays.

  • SetPartitions(n::Int, m::Int)

Return all set partitions of the elements of the array ${1,2,3,...,n}$ into exactly $m$ subsets, represented as arrays of arrays.

  • SetNumber(n::Int)

Return the numbers of partitions of an $n$-set into nonempty subsets.

  • SetNumber(n::Int, m::Int)

Return the numbers of partitions of an $n$-set into $m$ nonempty subsets.

🔶  SpigotPi

Computes the first n decimal digits of Pi, uses a variant of the spigot algorithm valid as long as the number of digits <= 54900. Based on ideas of A. Sale (1968). Algorithm due to D. Saada (1988) and S. Rabinowitz (1991). Proof due to Rabinowitz and S. Wagon (1995).

  • Pi, V000796

🔶  StirlingLahNumbers

  • T132393, L132393, V132393, M132393, T048993, L048993, V048993, M048993, T271703, L271703, V271703, M271703, T094587, L094587, V094587, M094587, T008279, L008279, V008279, M008279

🔶  SwingFactorial

Basic implementation of the swing algorithm using no primes. Claims to be the most efficient simple algorithm to compute the factorial. An advanced version based on prime-factorization is available as the prime-swing factorial factorialPS.

  • Sfactorial

🔶  Triangles

  • Triangle, ZTriangle, QTriangle, RecTriangle, TriangularNumber, isTriangular, assertTriangular, ShowAsΔ, ShowAsMatrix, Row, RowSums, fromΔ, toΔ, TriangleToList

🔶  UlamNumbers

An Ulam number $u(n)$ is the least number $> u(n-1)$ which is a unique sum of two distinct earlier terms; $u(1) = 1$ and $u(2) = 2$.

  • UlamList, isUlam, L002858

🔶  ZumkellerNumbers

A Zumkeller number $n$ is an integer whose divisors can be partitioned into two disjoint sets whose sums are both $σ(n)/2$.

  • isZumkeller, is083207, I083207, F083207, L083207, V083207