A368440 Expansion of e.g.f. exp(x) / (3 - 2*exp(3*x)).
1, 7, 103, 2287, 67687, 2504047, 111163303, 5757411247, 340788559207, 22693176094447, 1679047763217703, 136654363293340207, 12133120656211741927, 1167034341869994747247, 120886955198779063694503, 13416476227330202250197167, 1588276885073067052758303847
Offset: 0
Keywords
Programs
-
PARI
a_vector(n) = my(v=vector(n+1)); for(i=0, n, v[i+1]=1+2*sum(j=1, i, 3^j*binomial(i, j)*v[i-j+1])); v;
Formula
a(n) = 1 + 2 * Sum_{k=1..n} 3^k * binomial(n,k) * a(n-k).