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 A275245 #16 May 28 2024 01:06:07 %S A275245 10,20,40,42,50,60,80,84,100,114,120,126,136,156,160,168,180,200,220, %T A275245 228,240,250,252,272,294,300,312,320,336,342,360,378,400,440,444,456, %U A275245 468,480,500,504,540,544,588,600,624,640,672,684,720,756,800,816 %N A275245 Numbers k such that phi(k) divides k^2 while phi(k) does not divide k. %H A275245 Amiram Eldar, <a href="/A275245/b275245.txt">Table of n, a(n) for n = 1..10000</a> %e A275245 10 is a term because phi(10) = 4; 10 mod 4 = 2 and 10^2 mod 4 = 0. %t A275245 Select[Range[10^3], Function[k, And[Divisible[#^2, k], ! Divisible[#, k]]]@ EulerPhi@ # &] (* _Michael De Vlieger_, Jul 21 2016 *) %o A275245 (PARI) isok(n) = (n % eulerphi(n) != 0) && (n^2 % eulerphi(n) == 0) %Y A275245 Cf. A000010, A007694, A090778. %K A275245 nonn %O A275245 1,1 %A A275245 _Altug Alkan_, Jul 21 2016