A032307 Shifts left 2 places under "EFK" (unordered, size, unlabeled) transform.

1, 1, 1, 1, 2, 2, 4, 6, 10, 17, 29, 50, 88, 156, 279, 498, 909, 1639, 3010, 5495, 10152, 18674, 34745, 64312, 120197, 223850, 420057, 785683, 1480429, 2779462, 5253203, 9899964, 18761327, 35461501, 67383407, 127689713

Offset

1,5

Links

Andrew Howroyd, Table of n, a(n) for n = 1..500

Formula

G.f.: x + x^2 * exp(Sum_{n>=1} Sum_{k>=1} (-1)^(k+1) * a(n)^k * x^(n*k) / k). - Ilya Gutkovskiy, Jun 30 2021

Prog

(PARI)
EFK(p, n)={prod(k=1, n, 1 + polcoef(p, k)*x^k + O(x*x^n))}
seq(n)={my(p=O(1)); for(i=0, (n-1)\2, p=1+x*EFK(x*p, 2*i)); Vec(p+O(x^n))} \\ Andrew Howroyd, Sep 20 2018

Crossrefs

Cf. A032305.

Sequence in context: A293673 A344707 A293505 * A007560 A032237 A276061

Adjacent sequences: A032304 A032305 A032306 * A032308 A032309 A032310

Keyword

nonn

Author

Christian G. Bower

Status

approved