a(n) = n^7*(n^3 + 1)/2.

Terms

a(0) =0a(1) =1a(2) =576a(3) =30618a(4) =532480a(5) =4921875a(6) =30373056a(7) =141649396a(8) =537919488a(9) =1745783685a(10) =5005000000a(11) =12978455886a(12) =30976598016a(13) =68960620183a(14) =144680034240a(15) =288410625000a(16) =549890031616