Numbers k such that sigma(k) and sigma(k^3) are both primes.

Terms

a(0) =4a(1) =9a(2) =16a(3) =25a(4) =64a(5) =289a(6) =2401a(7) =7921a(8) =3418801a(9) =19439281a(10) =24730729a(11) =40819321a(12) =52258441a(13) =67848169a(14) =75151561a(15) =76405081a(16) =142396489a(17) =175006441a(18) =185313769a(19) =198443569a(20) =253541929a(21) =352425529a(22) =369062521a(23) =386554921a(24) =414896161a(25) =499477801a(26) =526105969a(27) =684921241a(28) =775678201