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

Terms

a(0) =0a(1) =1a(2) =8a(3) =49a(4) =176a(5) =465a(6) =1016a(7) =1953a(8) =3424a(9) =5601a(10) =8680a(11) =12881a(12) =18448a(13) =25649a(14) =34776a(15) =46145a(16) =60096a(17) =76993a(18) =97224a(19) =121201a(20) =149360a(21) =182161a(22) =220088a(23) =263649a(24) =313376a(25) =369825a(26) =433576a(27) =505233a(28) =585424a(29) =674801