OFFSET
0,2
FORMULA
a(n) = n! * Sum_{k=0..n} A000670(k) / k!.
a(0) = 1; a(n) = 2 * n * a(n-1) - Sum_{k=2..n} binomial(n,k) * (k-1) * a(n-k).
a(n) ~ n! / (2 * (1 - log(2)) * log(2)^(n+1)). - Vaclav Kotesovec, Aug 09 2021
MATHEMATICA
nmax = 20; CoefficientList[Series[1/((1 - x) (2 - Exp[x])), {x, 0, nmax}], x] Range[0, nmax]!
Table[n! Sum[HurwitzLerchPhi[1/2, -k, 0]/(2 k!), {k, 0, n}], {n, 0, 20}]
a[0] = 1; a[n_] := a[n] = 2 n a[n - 1] - Sum[Binomial[n, k] (k - 1) a[n - k], {k, 2, n}]; Table[a[n], {n, 0, 20}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Aug 10 2020
STATUS
approved