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 A367840 #8 Dec 02 2023 08:12:44
%S A367840 1,3,34,514,10456,265704,8103120,288302480,11722944896,536262671488,
%T A367840 27256865214208,1523936708699904,92949383868668928,
%U A367840 6141694449341637632,437033351625771001856,33319937543640487708672,2709708041047388536274944
%N A367840 Expansion of e.g.f. 1/(2 + x - exp(4*x)).
%F A367840 a(0) = 1; a(n) = -n * a(n-1) + Sum_{k=1..n} 4^k * binomial(n,k) * a(n-k).
%o A367840 (PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=-i*v[i]+sum(j=1, i, 4^j*binomial(i, j)*v[i-j+1])); v;
%Y A367840 Cf. A032032, A367838, A367839.
%Y A367840 Cf. A367786, A367837.
%K A367840 nonn
%O A367840 0,2
%A A367840 _Seiichi Manyama_, Dec 02 2023