a(n) = (1/6)*(2*n - 3)*(n + 2)*(n + 1).

Terms

a(0) =0a(1) =0a(2) =-1a(3) =-1a(4) =2a(5) =10a(6) =25a(7) =49a(8) =84a(9) =132a(10) =195a(11) =275a(12) =374a(13) =494a(14) =637a(15) =805a(16) =1000a(17) =1224a(18) =1479a(19) =1767a(20) =2090a(21) =2450a(22) =2849a(23) =3289a(24) =3772a(25) =4300a(26) =4875a(27) =5499a(28) =6174a(29) =6902