Numbers k>1 such that phi(phi(k)) = sigma(sopf(k)).

Terms

a(0) =40a(1) =50a(2) =54a(3) =171a(4) =195a(5) =231a(6) =330a(7) =377a(8) =387a(9) =518a(10) =638a(11) =742a(12) =745a(13) =888a(14) =1057a(15) =1141a(16) =1397a(17) =1561a(18) =1788a(19) =2422a(20) =2682a(21) =2763a(22) =3206a(23) =3357a(24) =3805a(25) =4037a(26) =4344a(27) =4382a(28) =4915a(29) =5093