a(n) = 6+32*n^2+8*n*(7+8*n^2)/3.

Terms

a(0) =6a(1) =78a(2) =342a(3) =926a(4) =1958a(5) =3566a(6) =5878a(7) =9022a(8) =13126a(9) =18318a(10) =24726a(11) =32478a(12) =41702a(13) =52526a(14) =65078a(15) =79486a(16) =95878a(17) =114382a(18) =135126a(19) =158238a(20) =183846a(21) =212078a(22) =243062a(23) =276926a(24) =313798a(25) =353806a(26) =397078a(27) =443742a(28) =493926a(29) =547758