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 A049197 #19 Feb 12 2021 04:50:51 %S A049197 5,10,13,15,17,19,21,26,29,30,33,34,35,37,38,39,41,42,51,53,55,57,58, %T A049197 61,65,66,69,70,73,74,77,78,82,85,87,89,91,93,95,97,101,102,105,106, %U A049197 109,110,111,113,114,115,119,122,123,127,129,130,133,137,138,141,143 %N A049197 Squarefree numbers whose Euler totient function is not squarefree. %C A049197 Numbers k such that abs(mu(k)) = 1 and mu(phi(k)) = 0. %H A049197 Amiram Eldar, <a href="/A049197/b049197.txt">Table of n, a(n) for n = 1..10000</a> %e A049197 110 = 2*5*11 is squarefree but phi(110) = 40 is divisible by a square, so 110 is in the sequence. %t A049197 Select[Range[144], SquareFreeQ[#] && !SquareFreeQ[EulerPhi[#]] &] (* _Amiram Eldar_, Feb 12 2021 *) %o A049197 (PARI) isok(k) = issquarefree(k) && !issquarefree(eulerphi(k)); \\ _Michel Marcus_, Feb 12 2021 %Y A049197 Cf. A000010, A005117, A013929, A049195, A049196. %K A049197 nonn %O A049197 1,1 %A A049197 _Labos Elemer_