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

Terms

a(0) =0a(1) =0a(2) =1a(3) =12a(4) =54a(5) =160a(6) =375a(7) =756a(8) =1372a(9) =2304a(10) =3645a(11) =5500a(12) =7986a(13) =11232a(14) =15379a(15) =20580a(16) =27000a(17) =34816a(18) =44217a(19) =55404a(20) =68590a(21) =84000a(22) =101871a(23) =122452a(24) =146004a(25) =172800a(26) =203125a(27) =237276a(28) =275562a(29) =318304