Numbers k such that gcd(phi(k), k-1) = number of distinct prime factors of (k-1).

Terms

a(0) =4a(1) =6a(2) =8a(3) =10a(4) =12a(5) =14a(6) =15a(7) =18a(8) =20a(9) =24a(10) =26a(11) =27a(12) =30a(13) =32a(14) =35a(15) =38a(16) =39a(17) =42a(18) =44a(19) =48a(20) =50a(21) =51a(22) =54a(23) =55a(24) =60a(25) =62a(26) =63a(27) =68a(28) =72a(29) =74