This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A069946 #21 Sep 05 2020 13:27:20 %S A069946 2,12,48,60,63,75,175,192,363,405,468,704,768,816,867,891,960,980, %T A069946 1008,1020,1587,1875,2023,2107,2331,2475,2523,2527,2800,2835,3072, %U A069946 3075,3185,3332,3757,4100,4335,4477,4851,5043,5780,6171,6292,6627,6727,6877,7220 %N A069946 Numbers k such that phi(k) mod core(k) = 1 where core(k) is the squarefree part of k. %C A069946 This sequence is infinite. For example, 3*4^k is a term for all k > 0, since core(3*4^k) = 3, phi(3*4^k) = 4^k and 4^k == 1 (mod 3). - _Amiram Eldar_, Sep 03 2020 %H A069946 Amiram Eldar, <a href="/A069946/b069946.txt">Table of n, a(n) for n = 1..10000</a> %t A069946 core[n_] := Times @@ (First[#]^Mod[Last[#], 2] & /@ FactorInteger[n]); Select[Range[10^4], Mod[EulerPhi[#], core[#]] == 1 &] (* _Amiram Eldar_, Sep 03 2020 *) %o A069946 (PARI) for(n=1,15000,if(eulerphi(n)%core(n)==1,print1(n,","))) %Y A069946 Cf. A000010, A002001, A007913. %K A069946 easy,nonn %O A069946 1,1 %A A069946 _Benoit Cloitre_, Apr 27 2002 %E A069946 Name corrected by _Amiram Eldar_, Sep 05 2020