a(n) = n*(6*n^4 + 8*n^3 + 1 - (-1)^n)/16.

Terms

a(0) =0a(1) =1a(2) =20a(3) =132a(4) =512a(5) =1485a(6) =3564a(7) =7504a(8) =14336a(9) =25425a(10) =42500a(11) =67716a(12) =103680a(13) =153517a(14) =220892a(15) =310080a(16) =425984a(17) =574209a(18) =761076a(19) =993700a(20) =1280000a(21) =1628781a(22) =2049740a(23) =2553552a(24) =3151872a(25) =3857425a(26) =4684004a(27) =5646564a(28) =6761216a(29) =8045325