This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A377580 #9 Nov 02 2024 09:12:56
%S A377580 1,2,6,66,920,17450,425772,12443438,428469456,16947065682,
%T A377580 757343738900,37752522755222,2076633137032632,124956870908294906,
%U A377580 8165077881669520476,575775223046122068510,43582446983541508540832,3524622951250814296207010,303306411871327203664657956
%N A377580 E.g.f. satisfies A(x) = (1 + x * exp(x*A(x)^2))^2.
%F A377580 E.g.f.: B(x)^2, where B(x) is the e.g.f. of A377581.
%F A377580 a(n) = n! * Sum_{k=0..n} k^(n-k) * binomial(4*n-4*k+2,k)/( (2*n-2*k+1)*(n-k)! ).
%o A377580 (PARI) a(n) = n!*sum(k=0, n, k^(n-k)*binomial(4*n-4*k+2, k)/((2*n-2*k+1)*(n-k)!));
%Y A377580 Cf. A377579, A377581.
%K A377580 nonn
%O A377580 0,2
%A A377580 _Seiichi Manyama_, Nov 02 2024