a(n) = n*(n + 1)*(5*n^2 + 5*n - 4)/12.

Terms

a(0) =0a(1) =1a(2) =13a(3) =56a(4) =160a(5) =365a(6) =721a(7) =1288a(8) =2136a(9) =3345a(10) =5005a(11) =7216a(12) =10088a(13) =13741a(14) =18305a(15) =23920a(16) =30736a(17) =38913a(18) =48621a(19) =60040a(20) =73360a(21) =88781a(22) =106513a(23) =126776a(24) =149800a(25) =175825a(26) =205101a(27) =237888a(28) =274456a(29) =315085