OFFSET
0,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..100
PROG
(PARI) a(n)={my(v=vector((n+1)\2+1, i, i--; (2*i)!/(2^i*i!))); if(n%2, 3, 1)*sum(i=0, n\2, sum(j=0, n\2, sum(k=abs(i-j), min(i+j, n-i-j), n!/((i+k-j)!*(i+j-k)!*(n-i-j-k)!*(j+k-i)!)*v[1+(n+1)\2-i]*v[1+j]*v[1+k] )))} \\ Andrew Howroyd, Mar 14 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, Feb 21 2021
STATUS
approved