OFFSET
0,3
FORMULA
a(0) = 1; a(n) = -Sum_{k=1..n} (-1)^k * binomial(n-1,k-1) * A009435(k) * a(n-k).
a(n) ~ n! / (Gamma(1/cosh(1)) * n^(1 - 1/cosh(1))). - Vaclav Kotesovec, Feb 24 2022
MATHEMATICA
nmax = 22; CoefficientList[Series[1/(1 - x)^Sech[x], {x, 0, nmax}], x] Range[0, nmax]!
PROG
(PARI) my(x='x+O('x^30)); Vec(serlaplace(1/(1-x)^(1/cosh(x)))) \\ Michel Marcus, Feb 23 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Feb 23 2022
STATUS
approved