Numbers n such that both sigma(n) and sigma(n) - 2 are primes.

Terms

a(0) =4a(1) =9a(2) =16a(3) =25a(4) =729a(5) =1681a(6) =3481a(7) =7921a(8) =10201a(9) =17161a(10) =552049a(11) =579121a(12) =1423249a(13) =5812921a(14) =7091569a(15) =7447441a(16) =9066121a(17) =9765625a(18) =10374841a(19) =10569001a(20) =11895601a(21) =22572001a(22) =38105929a(23) =43546801a(24) =46689889a(25) =52258441a(26) =75151561a(27) =82065481a(28) =86918329a(29) =90649441