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 A370086 #7 Feb 09 2024 01:46:52
%S A370086 1,1,4,40,796,27196,1437136,108931264,11207616400,1502077491856,
%T A370086 254091983968576,52922687300496256,13303823750214614464,
%U A370086 3970706309867394765760,1387875547214097148600576,561507863501525383223535616,260328000140228961840632033536
%N A370086 Expansion of e.g.f. exp( Sum_{k>=1} (2*k)!/k! * (x/2)^k/k ).
%F A370086 a(0) = 1; a(n) = (1/n) * Sum_{k=1..n} (2*k)!/2^k * binomial(n,k) * a(n-k).
%o A370086 (PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(exp(sum(k=1, N, (2*k)!/k!*(x/2)^k/k))))
%Y A370086 Cf. A000680, A370084.
%K A370086 nonn
%O A370086 0,3
%A A370086 _Seiichi Manyama_, Feb 08 2024