a(n) = n*(7*n^2-4)/3.

Terms

a(0) =0a(1) =1a(2) =16a(3) =59a(4) =144a(5) =285a(6) =496a(7) =791a(8) =1184a(9) =1689a(10) =2320a(11) =3091a(12) =4016a(13) =5109a(14) =6384a(15) =7855a(16) =9536a(17) =11441a(18) =13584a(19) =15979a(20) =18640a(21) =21581a(22) =24816a(23) =28359a(24) =32224a(25) =36425a(26) =40976a(27) =45891a(28) =51184a(29) =56869