OFFSET
0,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..450
FORMULA
a(n) = n! * Sum_{k=0..n-1} 4^k / ((n-k) * k!).
a(n) ~ exp(4) * (n-1)!. - Vaclav Kotesovec, Aug 09 2021
a(0) = 0, a(1) = 1, a(n) = (n+3) * a(n-1) - 4 * (n-1) * a(n-2) + 4^(n-1). - Seiichi Manyama, May 27 2022
MATHEMATICA
nmax = 22; CoefficientList[Series[-Log[1 - x] Exp[4 x], {x, 0, nmax}], x] Range[0, nmax]!
Table[n! Sum[4^k/((n - k) k!), {k, 0, n - 1}], {n, 0, 22}]
PROG
(PARI) a_vector(n) = my(v=vector(n+1)); v[1]=0; v[2]=1; for(i=2, n, v[i+1]=(i+3)*v[i]-4*(i-1)*v[i-1]+4^(i-1)); v; \\ Seiichi Manyama, May 27 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jul 15 2021
STATUS
approved