a(n) = n^2*(n-1)^3/4.

Terms

a(0) =0a(1) =0a(2) =1a(3) =18a(4) =108a(5) =400a(6) =1125a(7) =2646a(8) =5488a(9) =10368a(10) =18225a(11) =30250a(12) =47916a(13) =73008a(14) =107653a(15) =154350a(16) =216000a(17) =295936a(18) =397953a(19) =526338a(20) =685900a(21) =882000a(22) =1120581a(23) =1408198a(24) =1752048a(25) =2160000a(26) =2640625a(27) =3203226a(28) =3857868a(29) =4615408