# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a039767 Showing 1-1 of 1 %I A039767 #13 Sep 16 2024 02:50:18 %S A039767 4,6,8,10,12,14,15,18,20,24,26,27,30,32,35,38,39,42,44,48,50,51,54,55, %T A039767 60,62,63,68,72,74,75,80,81,82,84,87,90,95,98,99,102,104,108,110,114, %U A039767 119,122,123,126,128,132,135,138,140,143,147,150,152,158,159,164,168 %N A039767 Numbers k such that gcd(phi(k), k-1) = number of distinct prime factors of (k-1). %C A039767 If k = p+1 where p is an odd prime, then k is a term. - _Amiram Eldar_, Sep 16 2024 %H A039767 Amiram Eldar, Table of n, a(n) for n = 1..10000 %e A039767 phi(15) = 8, gcd(8, 14) = 2, 14 = 2*7, 2 prime factors. %t A039767 q[k_] := GCD[EulerPhi[k], k-1] == PrimeNu[k-1]; Select[Range[200], q] (* _Amiram Eldar_, Sep 16 2024 *) %o A039767 (PARI) is(k) = k > 1 && gcd(eulerphi(k), k-1) == omega(k-1); \\ _Amiram Eldar_, Sep 16 2024 %Y A039767 Cf. A000010, A001221, A049559, A209211. %K A039767 nonn,easy %O A039767 1,1 %A A039767 _Olivier Gérard_ # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE