Numbers n such that sigma(n) is a power of prime (of the form p^a, p prime, a>=1).

Terms

a(0) =2a(1) =3a(2) =4a(3) =7a(4) =9a(5) =16a(6) =21a(7) =25a(8) =31a(9) =64a(10) =81a(11) =93a(12) =127a(13) =217a(14) =289a(15) =381a(16) =400a(17) =651a(18) =729a(19) =889a(20) =1681a(21) =2401a(22) =2667a(23) =3481a(24) =3937a(25) =4096a(26) =5041a(27) =7921a(28) =8191a(29) =10201