OFFSET
1,4
FORMULA
Recurrence: a(n+1) = Sum_{k=1..n} binomial(n,k)*(-k)^(n-k)*a(k).
MATHEMATICA
terms = 21; A[_] = 0; Do[A[x_] = Normal[Integrate[1 + A[x Exp[-x] + O[x]^(terms + 1)], x] + O[x]^(terms + 1)], terms]; Rest[CoefficientList[A[x], x] Range[0, terms]!]
a[n_] := a[n] = Sum[Binomial[n - 1, k] (-k)^(n - k - 1) a[k], {k, 1, n - 1}]; a[1] = 1; Table[a[n], {n, 1, 21}]
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, May 04 2019
STATUS
approved