A032307 - OEIS

%I #10 Jul 02 2021 16:43:27

%S 1,1,1,1,2,2,4,6,10,17,29,50,88,156,279,498,909,1639,3010,5495,10152,

%T 18674,34745,64312,120197,223850,420057,785683,1480429,2779462,

%U 5253203,9899964,18761327,35461501,67383407,127689713

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

%H Andrew Howroyd, <a href="/A032307/b032307.txt">Table of n, a(n) for n = 1..500</a>

%F 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

%o (PARI)

%o EFK(p,n)={prod(k=1, n, 1 + polcoef(p,k)*x^k + O(x*x^n))}

%o 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

%Y Cf. A032305.

%K nonn

%O 1,5

%A _Christian G. Bower_