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

Terms

a(0) =0a(1) =5a(2) =16a(3) =35a(4) =64a(5) =105a(6) =160a(7) =231a(8) =320a(9) =429a(10) =560a(11) =715a(12) =896a(13) =1105a(14) =1344a(15) =1615a(16) =1920a(17) =2261a(18) =2640a(19) =3059a(20) =3520a(21) =4025a(22) =4576a(23) =5175a(24) =5824a(25) =6525a(26) =7280a(27) =8091a(28) =8960a(29) =9889