a(n) = n^2 * (4*n^2 - 1) / 3.

Terms

a(0) =0a(1) =1a(2) =20a(3) =105a(4) =336a(5) =825a(6) =1716a(7) =3185a(8) =5440a(9) =8721a(10) =13300a(11) =19481a(12) =27600a(13) =38025a(14) =51156a(15) =67425a(16) =87296a(17) =111265a(18) =139860a(19) =173641a(20) =213200a(21) =259161a(22) =312180a(23) =372945a(24) =442176a(25) =520625a(26) =609076a(27) =708345a(28) =819280a(29) =942761