OFFSET
0,4
FORMULA
a(n) = (-2)^n*Sum_{k=0..n} A109449(n, k)*(-1/2)^k.
From Vaclav Kotesovec, May 06 2021: (Start)
a(n) ~ (-1)^n * exp(-Pi/4) * 4^(n+1) * n! / Pi^(n+1).
E.g.f.: exp(x)*(1 - tan(x))/(1 + tan(x)). (End)
MAPLE
a := n -> add((-1)^k*binomial(n, k)*A000831(k), k=0..n):
seq(a(n), n = 0..21);
MATHEMATICA
Table[-1 + Sum[(-1)^k * Binomial[n, k] * 4^k * Abs[EulerE[k, 1/2] + EulerE[k, 1]], {k, 0, n}], {n, 0, 20}] (* Vaclav Kotesovec, May 06 2021 *)
CROSSREFS
KEYWORD
sign
AUTHOR
Peter Luschny, May 06 2021
STATUS
approved