a(n) = n^6*(n^5 + 1)/2.

Terms

a(0) =0a(1) =1a(2) =1056a(3) =88938a(4) =2099200a(5) =24421875a(6) =181421856a(7) =988722196a(8) =4295098368a(9) =15690795525a(10) =50000500000a(11) =142656721086a(12) =371505678336a(13) =896082610423