a(n) = binomial(3*n-1,n) * binomial(3*n,n)/(2*n+1).

A278884

a(n) = binomial(3*n-1,n) * binomial(3*n,n)/(2*n+1).

Terms

    a(0) =1a(1) =2a(2) =30a(3) =672a(4) =18150a(5) =546546a(6) =17672928a(7) =600935040a(8) =21212454582a(9) =770748371250

External references