OFFSET
0,3
FORMULA
a(n) = n! * Sum_{k=0..n} (-2 * (n-k+1))^k / k!.
a(0) = 1; a(n) = -n * a(n-1) - Sum_{k=2..n} binomial(n,k) * 2^k * a(n-k).
MATHEMATICA
nmax = 21; CoefficientList[Series[1/(Exp[2 x] - x), {x, 0, nmax}], x] Range[0, nmax]!
Table[n! Sum[(-2 (n - k + 1))^k/k!, {k, 0, n}], {n, 0, 21}]
a[0] = 1; a[n_] := a[n] = -n a[n - 1] - Sum[Binomial[n, k] 2^k a[n - k], {k, 2, n}]; Table[a[n], {n, 0, 21}]
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Aug 09 2020
STATUS
approved