OFFSET
0,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..200
FORMULA
From Vaclav Kotesovec, Oct 30 2021: (Start)
a(n) ~ 2^(2*n + 1/2) * n^n / exp(n - 3/2).
Recurrence: n*(2*n - 5)*a(n) = (2*n - 5)*(2*n - 1)*(2*n + 3)*a(n-1) - (2*n - 3)*(24*n^2 - 72*n + 29)*a(n-2) + (2*n - 9)*(2*n - 5)*(2*n - 1)*a(n-3) + (n-3)*(2*n - 1)*a(n-4). (End)
PROG
(PARI) a(n)=sum(i=0, n, sum(j=0, n, sum(k=0, n, if(i+j+k-n, 0, (n+i+j)!/(i+j)!/j!/k!))))
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Mar 25 2004
STATUS
approved