a(n) = n*(20 + 15*n + n^2)/6.

Terms

a(0) =6a(1) =18a(2) =37a(3) =64a(4) =100a(5) =146a(6) =203a(7) =272a(8) =354a(9) =450a(10) =561a(11) =688a(12) =832a(13) =994a(14) =1175a(15) =1376a(16) =1598a(17) =1842a(18) =2109a(19) =2400a(20) =2716a(21) =3058a(22) =3427a(23) =3824a(24) =4250a(25) =4706a(26) =5193a(27) =5712a(28) =6264a(29) =6850