Name |
First elements |
Short description |
OEIS
|
Kolakoski sequence
|
1, 2, 2, 1, 1, 2, 1, 2, 2, 1, ...
|
The nth term describes the length of the nth run
|
A000002
|
Euler's totient function φ(n)
|
1, 1, 2, 2, 4, 2, 6, 4, 6, 4, ...
|
φ(n) is the number of positive integers not greater than n that are coprime with n.
|
A000010
|
Lucas numbers L(n)
|
2, 1, 3, 4, 7, 11, 18, 29, 47, 76, ...
|
L(n) = L(n − 1) + L(n − 2) for n ≥ 2, with L(0) = 2 and L(1) = 1.
|
A000032
|
Prime numbers pn
|
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, ...
|
The prime numbers pn, with n ≥ 1. A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers.
|
A000040
|
Partition numbers Pn
|
1, 1, 2, 3, 5, 7, 11, 15, 22, 30, 42, ...
|
The partition numbers, number of additive breakdowns of n.
|
A000041
|
Fibonacci numbers F(n)
|
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...
|
F(n) = F(n − 1) + F(n − 2) for n ≥ 2, with F(0) = 0 and F(1) = 1.
|
A000045
|
Sylvester's sequence
|
2, 3, 7, 43, 1807, 3263443, 10650056950807, 113423713055421844361000443, ...
|
a(n + 1) = a(n)⋅a(n − 1)⋅ ⋯ ⋅a(0) + 1 = a(n) − a(n) + 1 for n ≥ 1, with a(0) = 2.
|
A000058
|
Tribonacci numbers
|
0, 1, 1, 2, 4, 7, 13, 24, 44, 81, ...
|
T(n) = T(n − 1) + T(n − 2) + T(n − 3) for n ≥ 3, with T(0) = 0 and T(1) = T(2) = 1.
|
A000073
|
Powers of 2
|
1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, ...
|
Powers of 2: 2 for n ≥ 0
|
A000079
|
Polyominoes
|
1, 1, 1, 2, 5, 12, 35, 108, 369, ...
|
The number of free polyominoes with n cells.
|
A000105
|
Catalan numbers Cn
|
1, 1, 2, 5, 14, 42, 132, 429, 1430, 4862, ...
|
|
A000108
|
Bell numbers Bn
|
1, 1, 2, 5, 15, 52, 203, 877, 4140, 21147, ...
|
Bn is the number of partitions of a set with n elements.
|
A000110
|
Euler zigzag numbers En
|
1, 1, 1, 2, 5, 16, 61, 272, 1385, 7936, ...
|
En is the number of linear extensions of the "zig-zag" poset.
|
A000111
|
Lazy caterer's sequence
|
1, 2, 4, 7, 11, 16, 22, 29, 37, 46, ...
|
The maximal number of pieces formed when slicing a pancake with n cuts.
|
A000124
|
Pell numbers Pn
|
0, 1, 2, 5, 12, 29, 70, 169, 408, 985, ...
|
a(n) = 2a(n − 1) + a(n − 2) for n ≥ 2, with a(0) = 0, a(1) = 1.
|
A000129
|
Factorials n!
|
1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, ...
|
n! = 1⋅2⋅3⋅4⋅ ⋯ ⋅n for n ≥ 1, with 0! = 1 (empty product).
|
A000142
|
Derangements
|
1, 0, 1, 2, 9, 44, 265, 1854, 14833, 133496, 1334961, 14684570, 176214841, ...
|
Number of permutations of n elements with no fixed points.
|
A000166
|
Divisor function σ(n)
|
1, 3, 4, 7, 6, 12, 8, 15, 13, 18, 12, 28, ...
|
σ(n) := σ1(n) is the sum of divisors of a positive integer n.
|
A000203
|
Fermat numbers Fn
|
3, 5, 17, 257, 65537, 4294967297, 18446744073709551617, 340282366920938463463374607431768211457, ...
|
Fn = 2 + 1 for n ≥ 0.
|
A000215
|
Polytrees
|
1, 1, 3, 8, 27, 91, 350, 1376, 5743, 24635, 108968, ...
|
Number of oriented trees with n nodes.
|
A000238
|
Perfect numbers
|
6, 28, 496, 8128, 33550336, 8589869056, 137438691328, 2305843008139952128, ...
|
n is equal to the sum s(n) = σ(n) − n of the proper divisors of n.
|
A000396
|
Ramanujan tau function
|
1, −24, 252, −1472, 4830, −6048, −16744, 84480, −113643, ...
|
Values of the Ramanujan tau function, τ(n) at n = 1, 2, 3, ...
|
A000594
|
Landau's function
|
1, 1, 2, 3, 4, 6, 6, 12, 15, 20, ...
|
The largest order of permutation of n elements.
|
A000793
|
Narayana's cows
|
1, 1, 1, 2, 3, 4, 6, 9, 13, 19, ...
|
The number of cows each year if each cow has one cow a year beginning its fourth year.
|
A000930
|
Padovan sequence
|
1, 1, 1, 2, 2, 3, 4, 5, 7, 9, ...
|
P(n) = P(n − 2) + P(n − 3) for n ≥ 3, with P(0) = P(1) = P(2) = 1.
|
A000931
|
Euclid–Mullin sequence
|
2, 3, 7, 43, 13, 53, 5, 6221671, 38709183810571, 139, ...
|
a(1) = 2; a(n + 1) is smallest prime factor of a(1) a(2) ⋯ a(n) + 1.
|
A000945
|
Lucky numbers
|
1, 3, 7, 9, 13, 15, 21, 25, 31, 33, ...
|
A natural number in a set that is filtered by a sieve.
|
A000959
|
Prime powers
|
2, 3, 4, 5, 7, 8, 9, 11, 13, 16, 17, 19, ...
|
Positive integer powers of prime numbers
|
A000961
|
Central binomial coefficients
|
1, 2, 6, 20, 70, 252, 924, ...
|
, numbers in the center of even rows of Pascal's triangle
|
A000984
|
Motzkin numbers
|
1, 1, 2, 4, 9, 21, 51, 127, 323, 835, ...
|
The number of ways of drawing any number of nonintersecting chords joining n (labeled) points on a circle.
|
A001006
|
Jordan–Pólya numbers
|
1, 2, 4, 6, 8, 12, 16, 24, 32, 36, 48, 64, ...
|
Numbers that are the product of factorials.
|
A001013
|
Jacobsthal numbers
|
0, 1, 1, 3, 5, 11, 21, 43, 85, 171, 341, ...
|
a(n) = a(n − 1) + 2a(n − 2) for n ≥ 2, with a(0) = 0, a(1) = 1.
|
A001045
|
Sum of proper divisors s(n)
|
0, 1, 1, 3, 1, 6, 1, 7, 4, 8, ...
|
s(n) = σ(n) − n is the sum of the proper divisors of the positive integer n.
|
A001065
|
Wedderburn–Etherington numbers
|
0, 1, 1, 1, 2, 3, 6, 11, 23, 46, ...
|
The number of binary rooted trees (every node has out-degree 0 or 2) with n endpoints (and 2n − 1 nodes in all).
|
A001190
|
Gould's sequence
|
1, 2, 2, 4, 2, 4, 4, 8, 2, 4, 4, 8, 4, 8, 8, ...
|
Number of odd entries in row n of Pascal's triangle.
|
A001316
|
Semiprimes
|
4, 6, 9, 10, 14, 15, 21, 22, 25, 26, ...
|
Products of two primes, not necessarily distinct.
|
A001358
|
Golomb sequence
|
1, 2, 2, 3, 3, 4, 4, 4, 5, 5, ...
|
a(n) is the number of times n occurs, starting with a(1) = 1.
|
A001462
|
Perrin numbers Pn
|
3, 0, 2, 3, 2, 5, 5, 7, 10, 12, ...
|
P(n) = P(n − 2) + P(n − 3) for n ≥ 3, with P(0) = 3, P(1) = 0, P(2) = 2.
|
A001608
|
Sorting number
|
0, 1, 3, 5, 8, 11, 14, 17, 21, 25, 29, 33, 37, 41, 45, 49, ...
|
Used in the analysis of comparison sorts.
|
A001855
|
Cullen numbers Cn
|
1, 3, 9, 25, 65, 161, 385, 897, 2049, 4609, 10241, 22529, 49153, 106497, ...
|
Cn = n⋅2 + 1, with n ≥ 0.
|
A002064
|
Primorials pn#
|
1, 2, 6, 30, 210, 2310, 30030, 510510, 9699690, 223092870, ...
|
pn#, the product of the first n primes.
|
A002110
|
Highly composite numbers
|
1, 2, 4, 6, 12, 24, 36, 48, 60, 120, ...
|
A positive integer with more divisors than any smaller positive integer.
|
A002182
|
Superior highly composite numbers
|
2, 6, 12, 60, 120, 360, 2520, 5040, 55440, 720720, ...
|
A positive integer n for which there is an e > 0 such that d(n)/n ≥ d(k)/k for all k > 1.
|
A002201
|
Pronic numbers
|
0, 2, 6, 12, 20, 30, 42, 56, 72, 90, ...
|
a(n) = 2t(n) = n(n + 1), with n ≥ 0 where t(n) are the triangular numbers.
|
A002378
|
Markov numbers
|
1, 2, 5, 13, 29, 34, 89, 169, 194, ...
|
Positive integer solutions of x + y + z = 3xyz.
|
A002559
|
Composite numbers
|
4, 6, 8, 9, 10, 12, 14, 15, 16, 18, ...
|
The numbers n of the form xy for x > 1 and y > 1.
|
A002808
|
Ulam number
|
1, 2, 3, 4, 6, 8, 11, 13, 16, 18, ...
|
a(1) = 1; a(2) = 2; for n > 2, a(n) is least number > a(n − 1) which is a unique sum of two distinct earlier terms; semiperfect.
|
A002858
|
Prime knots
|
0, 0, 1, 1, 2, 3, 7, 21, 49, 165, 552, 2176, 9988, ...
|
The number of prime knots with n crossings.
|
A002863
|
Carmichael numbers
|
561, 1105, 1729, 2465, 2821, 6601, 8911, 10585, 15841, 29341, ...
|
Composite numbers n such that a ≡ 1 (mod n) if a is coprime with n.
|
A002997
|
Woodall numbers
|
1, 7, 23, 63, 159, 383, 895, 2047, 4607, ...
|
n⋅2 − 1, with n ≥ 1.
|
A003261
|
Arithmetic numbers
|
1, 3, 5, 6, 7, 11, 13, 14, 15, 17, 19, 20, 21, 22, 23, 27, ...
|
An integer for which the average of its positive divisors is also an integer.
|
A003601
|
Colossally abundant numbers
|
2, 6, 12, 60, 120, 360, 2520, 5040, 55440, 720720, ...
|
A number n is colossally abundant if there is an ε > 0 such that for all k > 1,
where σ denotes the sum-of-divisors function.
|
A004490
|
Alcuin's sequence
|
0, 0, 0, 1, 0, 1, 1, 2, 1, 3, 2, 4, 3, 5, 4, 7, 5, 8, 7, 10, 8, 12, 10, 14, ...
|
Number of triangles with integer sides and perimeter n.
|
A005044
|
Deficient numbers
|
1, 2, 3, 4, 5, 7, 8, 9, 10, 11, ...
|
Positive integers n such that σ(n) < 2n.
|
A005100
|
Abundant numbers
|
12, 18, 20, 24, 30, 36, 40, 42, 48, 54, ...
|
Positive integers n such that σ(n) > 2n.
|
A005101
|
Untouchable numbers
|
2, 5, 52, 88, 96, 120, 124, 146, 162, 188, ...
|
Cannot be expressed as the sum of all the proper divisors of any positive integer.
|
A005114
|
Recamán's sequence
|
0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9, 24, 8, 25, 43, 62, ...
|
"subtract if possible, otherwise add": a(0) = 0; for n > 0, a(n) = a(n − 1) − n if that number is positive and not already in the sequence, otherwise a(n) = a(n − 1) + n, whether or not that number is already in the sequence.
|
A005132
|
Look-and-say sequence
|
1, 11, 21, 1211, 111221, 312211, 13112221, 1113213211, 31131211131221, 13211311123113112211, ...
|
A = 'frequency' followed by 'digit'-indication.
|
A005150
|
Practical numbers
|
1, 2, 4, 6, 8, 12, 16, 18, 20, 24, 28, 30, 32, 36, 40, ...
|
All smaller positive integers can be represented as sums of distinct factors of the number.
|
A005153
|
Alternating factorial
|
1, 1, 5, 19, 101, 619, 4421, 35899, 326981, 3301819, 36614981, 442386619, 5784634181, 81393657019, ...
|
n! − (n−1)! + (n−2)! − ... ± 1!.
|
A005165
|
Fortunate numbers
|
3, 5, 7, 13, 23, 17, 19, 23, 37, 61, ...
|
The smallest integer m > 1 such that pn# + m is a prime number, where the primorial pn# is the product of the first n prime numbers.
|
A005235
|
Semiperfect numbers
|
6, 12, 18, 20, 24, 28, 30, 36, 40, 42, ...
|
A natural number n that is equal to the sum of all or some of its proper divisors.
|
A005835
|
Magic constants
|
15, 34, 65, 111, 175, 260, 369, 505, 671, 870, 1105, 1379, 1695, 2056, ...
|
Sum of numbers in any row, column, or diagonal of a magic square of order n ≥ 3.
|
A006003
|
Weird numbers
|
70, 836, 4030, 5830, 7192, 7912, 9272, 10430, 10570, 10792, ...
|
A natural number that is abundant but not semiperfect.
|
A006037
|
Farey sequence numerators
|
0, 1, 0, 1, 1, 0, 1, 1, 2, 1, ...
|
|
A006842
|
Farey sequence denominators
|
1, 1, 1, 2, 1, 1, 3, 2, 3, 1, ...
|
|
A006843
|
Euclid numbers
|
2, 3, 7, 31, 211, 2311, 30031, 510511, 9699691, 223092871, ...
|
pn# + 1, i.e. 1 + product of first n consecutive primes.
|
A006862
|
Kaprekar numbers
|
1, 9, 45, 55, 99, 297, 703, 999, 2223, 2728, ...
|
X = Ab + B, where 0 < B < b and X = A + B.
|
A006886
|
Sphenic numbers
|
30, 42, 66, 70, 78, 102, 105, 110, 114, 130, ...
|
Products of 3 distinct primes.
|
A007304
|
Giuga numbers
|
30, 858, 1722, 66198, 2214408306, ...
|
Composite numbers so that for each of its distinct prime factors pi we have .
|
A007850
|
Radical of an integer
|
1, 2, 3, 2, 5, 6, 7, 2, 3, 10, ...
|
The radical of a positive integer n is the product of the distinct prime numbers dividing n.
|
A007947
|
Thue–Morse sequence
|
0, 1, 1, 0, 1, 0, 0, 1, 1, 0, ...
|
|
A010060
|
Regular paperfolding sequence
|
1, 1, 0, 1, 1, 0, 0, 1, 1, 1, ...
|
At each stage an alternating sequence of 1s and 0s is inserted between the terms of the previous sequence.
|
A014577
|
Blum integers
|
21, 33, 57, 69, 77, 93, 129, 133, 141, 161, 177, ...
|
Numbers of the form pq where p and q are distinct primes congruent to 3 (mod 4).
|
A016105
|
Magic numbers
|
2, 8, 20, 28, 50, 82, 126, ...
|
A number of nucleons (either protons or neutrons) such that they are arranged into complete shells within the atomic nucleus.
|
A018226
|
Superperfect numbers
|
2, 4, 16, 64, 4096, 65536, 262144, 1073741824, 1152921504606846976, 309485009821345068724781056, ...
|
Positive integers n for which σ(n) = σ(σ(n)) = 2n.
|
A019279
|
Bernoulli numbers Bn
|
1, −1, 1, 0, −1, 0, 1, 0, −1, 0, 5, 0, −691, 0, 7, 0, −3617, 0, 43867, 0, ...
|
|
A027641
|
Hyperperfect numbers
|
6, 21, 28, 301, 325, 496, 697, ...
|
k-hyperperfect numbers, i.e. n for which the equality n = 1 + k (σ(n) − n − 1) holds.
|
A034897
|
Achilles numbers
|
72, 108, 200, 288, 392, 432, 500, 648, 675, 800, ...
|
Positive integers which are powerful but imperfect.
|
A052486
|
Primary pseudoperfect numbers
|
2, 6, 42, 1806, 47058, 2214502422, 52495396602, ...
|
Satisfies a certain Egyptian fraction.
|
A054377
|
Erdős–Woods numbers
|
16, 22, 34, 36, 46, 56, 64, 66, 70, 76, 78, 86, 88, ...
|
The length of an interval of consecutive integers with property that every element has a factor in common with one of the endpoints.
|
A059756
|
Sierpinski numbers
|
78557, 271129, 271577, 322523, 327739, 482719, 575041, 603713, 903983, 934909, ...
|
Odd k for which { k⋅2 + 1 : n ∈ } consists only of composite numbers.
|
A076336
|
Riesel numbers
|
509203, 762701, 777149, 790841, 992077, ...
|
Odd k for which { k⋅2 − 1 : n ∈ } consists only of composite numbers.
|
A076337
|
Baum–Sweet sequence
|
1, 1, 0, 1, 1, 0, 0, 1, 0, 1, ...
|
a(n) = 1 if the binary representation of n contains no block of consecutive zeros of odd length; otherwise a(n) = 0.
|
A086747
|
Gijswijt's sequence
|
1, 1, 2, 1, 1, 2, 2, 2, 3, 1, ...
|
The nth term counts the maximal number of repeated blocks at the end of the subsequence from 1 to n−1
|
A090822
|
Carol numbers
|
−1, 7, 47, 223, 959, 3967, 16127, 65023, 261119, 1046527, ...
|
|
A093112
|
Juggler sequence
|
0, 1, 1, 5, 2, 11, 2, 18, 2, 27, ...
|
If n ≡ 0 (mod 2) then ⌊√n⌋ else ⌊n⌋.
|
A094683
|
Highly totient numbers
|
1, 2, 4, 8, 12, 24, 48, 72, 144, 240, ...
|
Each number k on this list has more solutions to the equation φ(x) = k than any preceding k.
|
A097942
|
Euler numbers
|
1, 0, −1, 0, 5, 0, −61, 0, 1385, 0, ...
|
|
A122045
|
Polite numbers
|
3, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15, 17, ...
|
A positive integer that can be written as the sum of two or more consecutive positive integers.
|
A138591
|
Erdős–Nicolas numbers
|
24, 2016, 8190, 42336, 45864, 392448, 714240, 1571328, ...
|
A number n such that there exists another number m and
|
A194472
|
Solution to Stepping Stone Puzzle
|
1, 16, 28, 38, 49, 60, ...
|
The maximal value a(n) of the stepping stone puzzle
|
A337663
|