Numbers k such that sigma(k)/k and sigma_3(k)/k are both integers.

Terms

a(0) =1a(1) =6a(2) =120a(3) =496a(4) =672a(5) =8128a(6) =30240a(7) =32760a(8) =523776a(9) =23569920a(10) =33550336a(11) =459818240a(12) =1379454720a(13) =1476304896a(14) =8589869056a(15) =31998395520a(16) =51001180160a(17) =66433720320a(18) =137438691328a(19) =153003540480a(20) =403031236608