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

Terms

a(0) =0a(1) =1a(2) =65a(3) =1095a(4) =8194a(5) =39065a(6) =139971a(7) =411775a(8) =1048580a(9) =2391489a(10) =5000005a(11) =9743591a(12) =17915910a(13) =31374265a(14) =52706759a(15) =85429695a(16) =134217736a(17) =205169345a(18) =306110025a(19) =446935879a(20) =640000010a(21) =900544281a(22) =1247178955a(23) =1702412735a(24) =2293235724a(25) =3051757825a(26) =4015905101