Binomial coefficient C(3n,n-5).

Terms

a(0) =1a(1) =18a(2) =210a(3) =2024a(4) =17550a(5) =142506a(6) =1107568a(7) =8347680a(8) =61523748a(9) =445891810a(10) =3190187286a(11) =22595200368a(12) =158753389900