a(n) = Sum_{k=1..n} ((3*n-k-1)/(2*n-k))*(3*n-k-2)!/((n-1)!*(n-1)!*(n-k)!).

A241193

a(n) = Sum_{k=1..n} ((3*n-k-1)/(2*n-k))*(3*n-k-2)!/((n-1)!*(n-1)!*(n-k)!).

Terms

    a(0) =1a(1) =11a(2) =181a(3) =3499a(4) =73501a(5) =1623467a(6) =37081045a(7) =867484331a(8) =20661914989a(9) =499049420011

External references