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 A072477 #7 Jun 18 2025 05:19:27
%S A072477 18,1800,352800,114307200,55324684800,37399486924800,
%T A072477 33659538232320000,38910426196561920000,56186655427835412480000,
%U A072477 99113260174701667614720000,209723658529668728672747520000,524309146324171821681868800000000,1528885470681285032024329420800000000
%N A072477 a(n) = (2*n)!*binomial(2*n,n)/8.
%H A072477 Michel Bousquet, Gilbert Labelle and Pierre Leroux, <a href="https://doi.org/10.1016/S0012-365X(99)00406-9">Enumeration of planar two-face maps</a>, Discrete Mathematics, 222 (2000), 1-25.
%F A072477 From _Amiram Eldar_, Jun 18 2025: (Start)
%F A072477 Sum_{n>=2} 1/a(n) = 2*Pi*L_0(1/2) - 2, where L is the modified Struve function.
%F A072477 Sum_{n>=2} (-1)^n/a(n) = 2 - 2*Pi*H_0(1/2), where H is the Struve function. (End)
%t A072477 a[n_] := (2*n)!*Binomial[2*n, n]/8; Array[a, 12, 2] (* _Amiram Eldar_, Jun 18 2025 *)
%o A072477 (PARI) a(n) = (2*n)!*binomial(2*n, n)/8; \\ _Amiram Eldar_, Jun 18 2025
%Y A072477 Cf. A000984, A122747.
%K A072477 nonn,easy
%O A072477 2,1
%A A072477 _N. J. A. Sloane_, Aug 02 2002