a(n) = n^4*(n^5 + 1)/2.

Terms

a(0) =0a(1) =1a(2) =264a(3) =9882a(4) =131200a(5) =976875a(6) =5039496a(7) =20178004a(8) =67110912a(9) =193713525a(10) =500005000a(11) =1178981166a(12) =2579900544a(13) =5302263967a(14) =10330542600a(15) =19221705000a(16) =34359771136a(17) =59293980009a(18) =99179697672a(19) =161343914050a(20) =256000080000