OFFSET
0,2
FORMULA
G.f.: Sum_{k>=0} (2*k * x)^k/(1 - 2*k * x).
a(n) = 2^n * A031971(n).
a(n) ~ c * 2^n * n^n, where c = 1/(1 - 1/exp(1)) = A185393. - Vaclav Kotesovec, Dec 07 2021
MATHEMATICA
a[n_] := Sum[If[k == n == 0, 1, (2*k)^n], {k, 0, n}]; Array[a, 18, 0] (* Amiram Eldar, Dec 07 2021 *)
PROG
(PARI) a(n) = sum(k=0, n, (2*k)^n);
(PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=0, N, (2*k*x)^k/(1-2*k*x)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 07 2021
STATUS
approved