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

Terms

a(0) =0a(1) =0a(2) =4a(3) =24a(4) =80a(5) =200a(6) =420a(7) =784a(8) =1344a(9) =2160a(10) =3300a(11) =4840a(12) =6864a(13) =9464a(14) =12740a(15) =16800a(16) =21760a(17) =27744a(18) =34884a(19) =43320a(20) =53200a(21) =64680a(22) =77924a(23) =93104a(24) =110400a(25) =130000a(26) =152100a(27) =176904a(28) =204624a(29) =235480