OFFSET
0,3
FORMULA
a(0) = 1; a(n) = Sum_{k=1..n} (-1)^k * binomial(n,k) * (2^(k - 1) - 2) * a(n-k).
a(n) ~ n! * (7 + 4*sqrt(3) + (-1)^n) / ((3+2*sqrt(3)) * (log(2+sqrt(3)))^(n+1)). - Vaclav Kotesovec, Dec 03 2019
MATHEMATICA
nmax = 23; CoefficientList[Series[Exp[x]/(2 - Cosh[x]), {x, 0, nmax}], x] Range[0, nmax]!
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Nov 28 2019
STATUS
approved