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 A355426 #11 Jul 02 2022 09:27:56
%S A355426 1,3,24,284,4476,88178,2084564,57493334,1812223276,64262620538,
%T A355426 2531993864004,109738634393534,5188538157065276,265761817180172498,
%U A355426 14659691726110341844,866403731832477234134,54619096812884242006476,3658454458052874579886058
%N A355426 Expansion of e.g.f. 1/(1 - Sum_{k=1..3} (exp(k*x) - 1)/k).
%F A355426 a(0) = 1; a(n) = Sum_{k=1..n} (1 + 2^(k-1) + 3^(k-1)) * binomial(n,k) * a(n-k).
%o A355426 (PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(1/(1-sum(k=1, 3, (exp(k*x)-1)/k))))
%o A355426 (PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=sum(j=1, i, (1+2^(j-1)+3^(j-1))*binomial(i, j)*v[i-j+1])); v;
%Y A355426 Column k=3 of A355427.
%Y A355426 Cf. A004701.
%K A355426 nonn
%O A355426 0,2
%A A355426 _Seiichi Manyama_, Jul 01 2022