OFFSET
0,4
LINKS
Eric Weisstein's MathWorld, Bell Polynomial.
FORMULA
For n > 0, a(n) = n! * [x^n] sin( sqrt(n) * (exp(x) - 1) )/sqrt(n).
For n > 0, a(n) = ( Bell_n(sqrt(n) * i) - Bell_n(-sqrt(n) * i) )/(2 * sqrt(n) * i), where Bell_n(x) is n-th Bell polynomial and i is the imaginary unit.
PROG
(PARI) a(n) = sum(k=0, (n-1)\2, (-n)^k*stirling(n, 2*k+1, 2));
(PARI) a(n) = if(n==0, 0, round(n!*polcoef(sin(sqrt(n)*(exp(x+x*O(x^n))-1))/sqrt(n), n)));
(PARI) Bell_poly(n, x) = exp(-x)*suminf(k=0, k^n*x^k/k!);
a(n) = if(n==0, 0, round((Bell_poly(n, sqrt(n)*I)-Bell_poly(n, -sqrt(n)*I))/(2*sqrt(n)*I)));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Oct 11 2022
STATUS
approved