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 A383207 #9 Apr 19 2025 10:04:14
%S A383207 0,0,1,9,71,575,4957,45829,454015,4804191,54094749,645720757,
%T A383207 8142419727,108110708511,1506969153757,21993472779461,335257957315199,
%U A383207 5325979566073919,87999598425114045,1509471498829147637,26835040585117438415,493677094649876461759,9384926300821643459133
%N A383207 Expansion of e.g.f. (exp(f(x)) - 1)^2 / 2, where f(x) = (exp(2*x) - 1)/2.
%F A383207 a(n) = Sum_{k=2..n} 2^(n-k) * Stirling2(n,k) * Stirling2(k,2).
%o A383207 (PARI) a(n) = sum(k=2, n, 2^(n-k)*stirling(n, k, 2)*stirling(k, 2, 2));
%Y A383207 Column k=2 of A383206.
%Y A383207 Cf. A000558.
%K A383207 nonn
%O A383207 0,4
%A A383207 _Seiichi Manyama_, Apr 19 2025