a(n) = n*(n+1)*(13*n+2)/6.

Terms

a(0) =0a(1) =5a(2) =28a(3) =82a(4) =180a(5) =335a(6) =560a(7) =868a(8) =1272a(9) =1785a(10) =2420a(11) =3190a(12) =4108a(13) =5187a(14) =6440a(15) =7880a(16) =9520a(17) =11373a(18) =13452a(19) =15770a(20) =18340a(21) =21175a(22) =24288a(23) =27692a(24) =31400a(25) =35425a(26) =39780a(27) =44478a(28) =49532a(29) =54955