a(n) = Sum_{k=0..floor(n/2)} binomial(3*n+k-1,k) * binomial(3*n+k,n-2*k).

A379086

a(n) = Sum_{k=0..floor(n/2)} binomial(3*n+k-1,k) * binomial(3*n+k,n-2*k).

Terms

    a(0) =1a(1) =3a(2) =21a(3) =174a(4) =1509a(5) =13443a(6) =121962a(7) =1120899a(8) =10401021a(9) =97230090a(10) =914283621a(11) =8638552464a(12) =81945757734a(13) =779949538176

External references