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

Terms

a(0) =0a(1) =2a(2) =576a(3) =17496a(4) =204800a(5) =1406250a(6) =6858432a(7) =26353376a(8) =84934656a(9) =239148450a(10) =605000000a(11) =1403076312a(12) =3027787776a(13) =6149354666a(14) =11859019200a(15) =21870000000a(16) =38788923392a(17) =66474865026a(18) =110505715776a(19) =178774347800a(20) =282240000000