Numbers k such that gcd(phi(k), k-1) = number of divisors of k.

Terms

a(0) =1a(1) =3a(2) =21a(3) =33a(4) =57a(5) =69a(6) =77a(7) =85a(8) =93a(9) =105a(10) =125a(11) =129a(12) =141a(13) =161a(14) =175a(15) =177a(16) =201a(17) =205a(18) =209a(19) =213a(20) =221a(21) =237a(22) =249a(23) =253a(24) =309a(25) =321a(26) =329a(27) =345a(28) =365a(29) =381