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

Terms

a(0) =1a(1) =11a(2) =18a(3) =75a(4) =172a(5) =372a(6) =482a(7) =732a(8) =3276a(9) =7965a(10) =13068a(11) =46476a(12) =103488a(13) =252240a(14) =727956a(15) =1795605a(16) =6030528a(17) =8769600a(18) =15436092a(19) =56747712a(20) =224518995a(21) =297780084a(22) =317961000a(23) =855489144a(24) =2691137721a(25) =58016937600a(26) =127198874880a(27) =228517311456a(28) =411814778112