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 A383436 #12 Apr 27 2025 09:55:25
%S A383436 1,4,17,90,562,4046,33042,302098,3058742,33986022,411230866,
%T A383436 5383385882,75816017838,1143072268942,18370804322282,313528393766946,
%U A383436 5663106612415462,107932149554271158,2164639221616216002,45571352034025600042,1004848312350264480926,23159361103691809941342
%N A383436 a(1) = 1; a(n) = 2 + n * Sum_{k=1..n-1} a(k).
%F A383436 E.g.f.: -2 - x/2 + (-9*x/2 + 2*exp(x))/(1-x)^2.
%F A383436 a(n) = -9*n/2 * n! + 2 * Sum_{k=0..n} (k+1)! * binomial(n,k) for n > 1.
%F A383436 a(n) = (n^2 * a(n-1) - 2)/(n-1) for n > 2.
%F A383436 a(n) = (n+2) * a(n-1) - (n-1) * a(n-2) for n > 3.
%o A383436 (PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(-2-x/2+(-9*x/2+2*exp(x))/(1-x)^2))
%Y A383436 Cf. A007808, A074143, A082425, A082427, A082428, A082430, A383437.
%Y A383436 Cf. A001339.
%K A383436 nonn
%O A383436 1,2
%A A383436 _Seiichi Manyama_, Apr 27 2025