a(n) = 2*(3*n+1)!/(2*n+2)!.

A370054

a(n) = 2*(3*n+1)!/(2*n+2)!.

Terms

    a(0) =1a(1) =2a(2) =14a(3) =180a(4) =3432a(5) =87360a(6) =2790720a(7) =107442720a(8) =4845456000a(9) =250637587200

External references