a(n) = (1/12)*(n+1)*(n^3+19*n^2+118*n+228).

Terms

a(0) =0a(1) =19a(2) =61a(3) =137a(4) =260a(5) =445a(6) =709a(7) =1071a(8) =1552a(9) =2175a(10) =2965a(11) =3949a(12) =5156a(13) =6617a(14) =8365a(15) =10435a(16) =12864a(17) =15691a(18) =18957a(19) =22705a(20) =26980a(21) =31829a(22) =37301a(23) =43447a(24) =50320a(25) =57975a(26) =66469a(27) =75861a(28) =86212a(29) =97585