Numbers k such that sigma(sigma(k)) = 2*phi(k).

Terms

a(0) =13a(1) =43a(2) =109a(3) =151a(4) =883a(5) =2143a(6) =116581a(7) =388537a(8) =1711663a(9) =2498227a(10) =4004107a(11) =5550331a(12) =12641137a(13) =13617361a(14) =18591967a(15) =20755393a(16) =22998397a(17) =26838523a(18) =29308291a(19) =34564351a(20) =36300841a(21) =44829073a(22) =82368469a(23) =149460841a(24) =184988197a(25) =238225003a(26) =252757891a(27) =340428853