OFFSET
0,3
COMMENTS
Sum of squares of products of terms in all partitions of n into distinct parts.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..10000
FORMULA
G.f.: exp(Sum_{k>=1} Sum_{j>=1} (-1)^(k+1)*j^(2*k)*x^(j*k)/k). - Ilya Gutkovskiy, Jun 14 2018
Conjecture: log(a(n)) ~ sqrt(2*n) * (log(2*n) - 2). - Vaclav Kotesovec, Dec 27 2020
EXAMPLE
The partitions of 6 into distinct parts are 6, 1+5, 2+4, 1+2+3, the corresponding squares of products are 36, 25, 64, 36 and their sum is a(6) = 161.
MAPLE
b:= proc(n, i) option remember; (m->
`if`(m<n, 0, `if`(n=m, i!^2, b(n, i-1)+
`if`(i>n, 0, i^2*b(n-i, i-1)))))(i*(i+1)/2)
end:
a:= n-> b(n$2):
seq(a(n), n=0..40); # Alois P. Heinz, Sep 10 2017
MATHEMATICA
Take[ CoefficientList[ Expand[ Product[1 + m^2*q^m, {m, 100}]], q], 31] (* Robert G. Wilson v, Apr 05 2005 *)
PROG
(PARI) N=66; x='x+O('x^N); Vec(prod(n=1, N, 1+n^2*x^n)) \\ Seiichi Manyama, Sep 10 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Jon Perry, Apr 04 2004
EXTENSIONS
More terms from Robert G. Wilson v, Apr 05 2004
STATUS
approved