a(n) = Sum_{k=0..floor(n/3)} binomial(3*n+k-1,k) * binomial(3*n+k,n-3*k).

A379087

a(n) = Sum_{k=0..floor(n/3)} binomial(3*n+k-1,k) * binomial(3*n+k,n-3*k).

Terms

    a(0) =1a(1) =3a(2) =15a(3) =93a(4) =651a(5) =4803a(6) =36177a(7) =275208a(8) =2108091a(9) =16243671a(10) =125817345a(11) =978933354a(12) =7646000421a(13) =59915086026a(14) =470820659940

External references