OFFSET
1,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..100
Eric Weisstein's World of Mathematics, Cocktail Party Graph
Eric Weisstein's World of Mathematics, Minimal Edge Cover
FORMULA
a(n) = Sum_{k=0..n} (-1)^(n-k) * binomial(n,k) * (2*k)! * [x^(2*k)] B(n-k,x), where B(k,x) = (2*exp(x) - 1)^k * exp(-x - x^2/2 + x*exp(x)). - Andrew Howroyd, Feb 21 2022
PROG
(PARI) a(n)={my(x=x+O(x^(2*n+1)), p=exp(-x - x^2/2 + x*exp(x)), q=2*exp(x) - 1); sum(k=0, n, (-1)^(n-k)*binomial(n, k)*(2*k)!*polcoef(q^(n-k)*p, 2*k))} \\ Andrew Howroyd, Feb 21 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Feb 14 2022
EXTENSIONS
Terms a(5) and beyond from Andrew Howroyd, Feb 21 2022
STATUS
approved