OFFSET
0,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..100
FORMULA
PROG
(PARI) \\ here b(n) is A000085.
b(n)={sum(k=0, n\2, n!/((n-2*k)!*2^k*k!))}
a(n)={my(v=vector(n+1, i, b(i-1))); sum(i=0, n, sum(j=0, n-i, sum(k=0, n-i-j, n!/(i!*j!*k!*(n-i-j-k)!)*v[1+n-i-j]*v[1+n-i-k]*v[1+n-j-k] )))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Feb 21 2021
STATUS
approved