OFFSET
2,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 2..200
FORMULA
a(n) = Sum_{i=0..floor((n-2)/3)} binomial(n-2+i, i)*binomial(4*n-4-i, n-2-3*i)/(n-1).
PROG
(PARI) a(n) = if(n>1, sum(i=0, floor((n-2)/3), binomial(n-2+i, i)*binomial(4*n-4-i, n-2-3*i))/(n-1)); \\ Andrew Howroyd, Nov 12 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved