a(n) = (n^3 + 24*n^2 + 65*n + 36)/6.

Terms

a(0) =6a(1) =21a(2) =45a(3) =79a(4) =124a(5) =181a(6) =251a(7) =335a(8) =434a(9) =549a(10) =681a(11) =831a(12) =1000a(13) =1189a(14) =1399a(15) =1631a(16) =1886a(17) =2165a(18) =2469a(19) =2799a(20) =3156a(21) =3541a(22) =3955a(23) =4399a(24) =4874a(25) =5381a(26) =5921a(27) =6495a(28) =7104a(29) =7749