Numbers k such that sigma_4(k)/sigma_2(k) is prime.

Terms

a(0) =4a(1) =9a(2) =20a(3) =25a(4) =169a(5) =289a(6) =961a(7) =1849a(8) =3721a(9) =6889a(10) =11881a(11) =14641a(12) =15625a(13) =17161a(14) =52441a(15) =57121a(16) =66049a(17) =69169a(18) =72361a(19) =96721a(20) =97969a(21) =117649a(22) =130321a(23) =196249a(24) =214369a(25) =253009a(26) =326041a(27) =351649a(28) =358801a(29) =383161