OFFSET
0,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..200
Eric Weisstein's World of Mathematics, Bell Polynomial.
FORMULA
a(n) = Sum_{k=0..floor(n/2)} (-4)^k * Stirling2(n,2*k).
a(n) = 1; a(n) = -4 * Sum_{k=0..n-1} binomial(n-1, k) * A357738(k).
a(n) = ( Bell_n(2 * i) + Bell_n(-2 * i) )/2, where Bell_n(x) is n-th Bell polynomial and i is the imaginary unit.
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(cos(2*(exp(x)-1))))
(PARI) a(n) = sum(k=0, n\2, (-4)^k*stirling(n, 2*k, 2));
(PARI) Bell_poly(n, x) = exp(-x)*suminf(k=0, k^n*x^k/k!);
a(n) = round((Bell_poly(n, 2*I)+Bell_poly(n, -2*I)))/2;
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Oct 10 2022
STATUS
approved