a(n) = (3*n)! / ((n+1)*(n!)^3).

A007004

a(n) = (3*n)! / ((n+1)*(n!)^3).

Terms

    a(0) =1a(1) =3a(2) =30a(3) =420a(4) =6930a(5) =126126a(6) =2450448a(7) =49884120a(8) =1051723530a(9) =22787343150a(10) =504636071940

External references