a(n) = n*(n^2 + 12*n - 25)/6.

Terms

a(0) =0a(1) =-2a(2) =1a(3) =10a(4) =26a(5) =50a(6) =83a(7) =126a(8) =180a(9) =246a(10) =325a(11) =418a(12) =526a(13) =650a(14) =791a(15) =950a(16) =1128a(17) =1326a(18) =1545a(19) =1786a(20) =2050a(21) =2338a(22) =2651a(23) =2990a(24) =3356a(25) =3750a(26) =4173a(27) =4626a(28) =5110a(29) =5626