OFFSET
1,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..200
FORMULA
a(n) = (Sum_{k=3..n} binomial(n,k)*(k-1)!) + (1/2)*Sum_{k=1..floor(n/2)} (k*binomial(n,2*k) * binomial(2*k,k) * (Sum_{j=0..n-2*k} binomial(n-2*k,j)*(k+j-1)!)^2).
PROG
(PARI) a(n)={sum(k=3, n, binomial(n, k)*(k-1)!) + sum(k=1, n\2, k*binomial(n, 2*k) * binomial(2*k, k) * sum(j=0, n-2*k, binomial(n-2*k, j)*(k+j-1)!)^2)/2}
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Feb 21 2021
STATUS
approved