OFFSET
0,4
FORMULA
a(0) = 1; a(n) = -Sum_{k=1..n} b(k) * binomial(n,k) * a(n-k), where b(k) = (-1)^((k+1)/2) * A000182((k+1)/2) if k is odd, otherwise 1.
MATHEMATICA
m = 21; Range[0, m]! * CoefficientList[Series[1/(Cosh[x] - Tanh[x]), {x, 0, m}], x] (* Amiram Eldar, Mar 06 2022 *)
PROG
(PARI) my(N=40, x='x+O('x^N)); Vec(serlaplace(1/(cosh(x)-tanh(x))))
(PARI) c(n) = ((-4)^n-(-16)^n)*bernfrac(2*n)/(2*n);
b(n) = if(n%2==1, (-1)^((n+1)/2)*c((n+1)/2), 1);
a(n) = if(n==0, 1, -sum(k=1, n, b(k)*binomial(n, k)*a(n-k)));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Mar 06 2022
STATUS
approved