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

Terms

a(0) =1a(1) =1a(2) =1045a(3) =23725a(4) =195661a(5) =975061a(6) =3578401a(7) =10680265a(8) =27453385a(9) =63016921a(10) =132361021a(11) =258815701a(12) =477132085a(13) =837244045a(14) =1408778281a(15) =2286380881a(16) =3595928401a(17) =5501691505a(18) =8214519205a(19) =12001111741a(20) =17194450141a(21) =24205450501a(22) =33535911025a(23) =45792819865a(24) =61704091801