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

Terms

a(0) =0a(1) =1a(2) =4a(3) =13a(4) =32a(5) =65a(6) =116a(7) =189a(8) =288a(9) =417a(10) =580a(11) =781a(12) =1024a(13) =1313a(14) =1652a(15) =2045a(16) =2496a(17) =3009a(18) =3588a(19) =4237a(20) =4960a(21) =5761a(22) =6644a(23) =7613a(24) =8672a(25) =9825a(26) =11076a(27) =12429a(28) =13888a(29) =15457