a(n) = n^7*(n^2 + 1)/2.

Terms

a(0) =0a(1) =1a(2) =320a(3) =10935a(4) =139264a(5) =1015625a(6) =5178816a(7) =20588575a(8) =68157440a(9) =196101729a(10) =505000000a(11) =1188717431a(12) =2597806080a(13) =5333623945a(14) =10383230144a(15) =19307109375a(16) =34493956096a(17) =59499107585a(18) =99485755200a(19) =161790784759a(20) =256640000000a(21) =398040567561a(22) =604881787840a(23) =902278743455