Numbers n such that sigma(n) - 1 and sigma(phi(n)) are both primes.

Terms

a(0) =3a(1) =5a(2) =6a(3) =10a(4) =17a(5) =34a(6) =40a(7) =60a(8) =85a(9) =136a(10) =204a(11) =240a(12) =4369a(13) =8224a(14) =8704a(15) =8738a(16) =10880a(17) =12336a(18) =13056a(19) =65537a(20) =131074a(21) =131584a(22) =139264a(23) =163840a(24) =164480a(25) =174760a(26) =208896a(27) =245760a(28) =262140a(29) =524296