OFFSET
0,10
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..3000
FORMULA
a(n) = [x^(2n) y^n] 1/Product_{j>=1} (1-y*x^A000217(j)).
a(n) = A319797(2n,n).
G.f.: Product_{k>=1} 1 / (1 - x^(k*(k + 3)/2)). - Ilya Gutkovskiy, Jan 31 2021
MAPLE
h:= proc(n) option remember; `if`(n<1, 0,
`if`(issqr(8*n+1), n, h(n-1)))
end:
b:= proc(n, i, k) option remember; `if`(n=0, `if`(k=0, 1, 0),
`if`(i*k<n or k>n, 0, b(n, h(i-1), k)+b(n-i, h(min(n-i, i)), k-1)))
end:
a:= n-> b(2*n, h(2*n), n):
seq(a(n), n=0..80);
MATHEMATICA
h[n_] := h[n] = If[n < 1, 0, If[IntegerQ@Sqrt[8*n + 1], n, h[n - 1]]];
b[n_, i_, k_] := b[n, i, k] = If[n == 0, If[k == 0, 1, 0], If[i*k < n || k > n, 0, b[n, h[i - 1], k] + b[n - i, h[Min[n - i, i]], k - 1]]];
a[n_] := b[2n, h[2n], n];
a /@ Range[0, 80] (* Jean-François Alcover, Mar 12 2021, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Sep 28 2018
STATUS
approved