OFFSET
0,3
LINKS
Robert Israel, Table of n, a(n) for n = 0..1000
FORMULA
a(n) ~ exp(sqrt(2*n/3) - 1/12 - c/6) * 6^(n - 1/4) / (2*sqrt(Pi)*n^(3/4)), where c = Sum_{j>=2} (-1)^j / (j * (6^(j-1) - 1)). - Vaclav Kotesovec, Apr 13 2021
MAPLE
N:= 100: # for a(0)..a(N)
G:= mul((1+x^k)^(6^(k-1)), k=1..N):
S:= series(G, x, N+1):
seq(coeff(S, x, k), k=0..N); # Robert Israel, Apr 12 2021
MATHEMATICA
nmax = 23; CoefficientList[Series[Product[(1 + x^k)^(6^(k - 1)), {k, 1, nmax}], {x, 0, nmax}], x]
a[n_] := a[n] = If[n == 0, 1, (1/n) Sum[Sum[(-1)^(k/d + 1) d 6^(d - 1), {d, Divisors[k]}] a[n - k], {k, 1, n}]]; Table[a[n], {n, 0, 23}]
PROG
(PARI) seq(n)={Vec(prod(k=1, n, (1 + x^k + O(x*x^n))^(6^(k-1))))} \\ Andrew Howroyd, Apr 12 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Apr 12 2021
STATUS
approved