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

Terms

a(0) =0a(1) =0a(2) =3a(3) =12a(4) =30a(5) =60a(6) =105a(7) =168a(8) =252a(9) =360a(10) =495a(11) =660a(12) =858a(13) =1092a(14) =1365a(15) =1680a(16) =2040a(17) =2448a(18) =2907a(19) =3420a(20) =3990a(21) =4620a(22) =5313a(23) =6072a(24) =6900a(25) =7800a(26) =8775a(27) =9828a(28) =10962a(29) =12180