A249035 Erroneous version of A249386.
4, 0, 0, 9, 9, 8, 8, 8, 3, 6, 9, 9, 9, 3, 7, 5, 3, 4, 2, 3, 0, 9, 5, 8
Offset: 0
This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
A planar partition of 13: 4 3 1 1 2 1 1 a(5) = (1/5!)*(sigma_2(1)^5+10*sigma_2(2)*sigma_2(1)^3+20*sigma_2(3)*sigma_2(1)^2+ 15*sigma_2(1)*sigma_2(2)^2+30*sigma_2(4)*sigma_2(1)+20*sigma_2(2)*sigma_2(3)+24*sigma_2(5)) = 24. - _Vladeta Jovovic_, Jan 10 2003 From _David Scambler_ and _Joerg Arndt_, May 01 2013: (Start) There are a(4) = 13 partitions of 4 objects of 2 colors ('b' and 'w'), each part containing at least one black object: 1 black part: [ bwww ] 2 black parts: [ bbww ] [ bww, b ] [ bw, bw ] 3 black parts: [ bbbw ] [ bbw, b ] [ bb, bw ] (but not: [bw, bb ] ) [ bw, b, b ] 4 black parts: [ bbbb ] [ bbb, b ] [ bb, bb ] [ bb, b, b ] [ b, b, b, b ] (End) From _Geoffrey Critzer_, Nov 29 2014: (Start) The corresponding partitions of the integer 4 are: 4''' 4'' 3'' + 1 2' + 2' 4' 3' + 1 2 + 2' 2' + 1 + 1 4 3 + 1 2 + 2 2 + 1 + 1 1 + 1 + 1 + 1. (End) From _Gus Wiseman_, Sep 25 2018: (Start) Non-isomorphic representatives of the a(4) = 13 chains of multisets whose dual is also a chain of multisets: {{1,1,1,1}} {{1,1,2,2}} {{1,2,2,2}} {{1,2,3,3}} {{1,2,3,4}} {{1},{1,1,1}} {{2},{1,2,2}} {{3},{1,2,3}} {{1,1},{1,1}} {{1,2},{1,2}} {{1},{1},{1,1}} {{2},{2},{1,2}} {{1},{1},{1},{1}} (End) G.f. = 1 + x + 3*x^2 + 6*x^3 + 13*x^4 + 24*x^5 + 48*x^6 + 86*x^7 + 160*x^8 + ...
using Nemo, Memoize @memoize function a(n) if n == 0 return 1 end s = sum(a(n - j) * divisor_sigma(j, 2) for j in 1:n) return div(s, n) end [a(n) for n in 0:20] # Peter Luschny, May 03 2020
series(mul((1-x^k)^(-k),k=1..64),x,63); # second Maple program: a:= proc(n) option remember; `if`(n=0, 1, add( a(n-j)*numtheory[sigma][2](j), j=1..n)/n) end: seq(a(n), n=0..50); # Alois P. Heinz, Aug 17 2015
CoefficientList[Series[Product[(1 - x^k)^-k, {k, 64}], {x, 0, 64}], x] Zeta[3]^(7/36)/2^(11/36)/Sqrt[3 Pi]/Glaisher E^(3 Zeta[3]^(1/3) (n/2)^(2/3) + 1/12)/n^(25/36) (* asymptotic formula after Wright; Vaclav Kotesovec, Jun 23 2014 *) a[0] = 1; a[n_] := a[n] = Sum[a[n - j] DivisorSigma[2, j], {j, n}]/n; Table[a[n], {n, 0, 50}] (* Jean-François Alcover, Sep 21 2015, after Alois P. Heinz *) CoefficientList[Series[Exp[Sum[DivisorSigma[2, n] x^n/n, {n, 50}]], {x, 0, 50}], x] (* Eric W. Weisstein, Feb 01 2018 *)
{a(n) = if( n<0, 0, polcoeff( exp( sum( k=1, n, x^k / (1 - x^k)^2 / k, x * O(x^n))), n))}; /* Michael Somos, Jan 29 2005 */
{a(n) = if( n<0, 0, polcoeff( prod( k=1, n, (1 - x^k + x * O(x^n))^-k), n))}; /* Michael Somos, Jan 29 2005 */
my(N=66, x='x+O('x^N)); Vec( prod(n=1,N, (1-x^n)^-n) ) \\ Joerg Arndt, Mar 25 2014
A000219(n)=#PlanePartitions(n) \\ See A091298 for PlanePartitions(). For illustrative use: much slower than the above. - M. F. Hasler, Sep 24 2018
from sympy import cacheit from sympy.ntheory import divisor_sigma @cacheit def A000219(n): if n <= 1: return 1 return sum(A000219(n - k) * divisor_sigma(k, 2) for k in range(1, n + 1)) // n print([A000219(n) for n in range(20)]) # R. J. Mathar, Oct 18 2009
# uses[EulerTransform from A166861] b = EulerTransform(lambda n: n) print([b(n) for n in range(37)]) # Peter Luschny, Nov 11 2020
2.009445660877013753064908765816434315885904689795...
b = 3*Zeta[3]^(1/3)/2^(2/3); RealDigits[b, 10, 102] // First
Comments