a(n) = n^2*(2*n^2 + 1)/3.

Terms

a(0) =0a(1) =1a(2) =12a(3) =57a(4) =176a(5) =425a(6) =876a(7) =1617a(8) =2752a(9) =4401a(10) =6700a(11) =9801a(12) =13872a(13) =19097a(14) =25676a(15) =33825a(16) =43776a(17) =55777a(18) =70092a(19) =87001a(20) =106800a(21) =129801a(22) =156332a(23) =186737a(24) =221376a(25) =260625a(26) =304876a(27) =354537a(28) =410032a(29) =471801