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 A385822 #36 Aug 22 2025 17:44:44 %S A385822 3,4,6,7,9,11,13,14,15,16,18,19,20,21,22,23,24,25,26,27,28,29,30,31, %T A385822 33,35,36,38,39,41,42,43,44,45,46,47,49,50,51,52,53,54,55,56,58,59,61, %U A385822 62,64,65,66,67,68,69,70,71,72,73,75,77,78,79,80,81,82,83,84,86,87,88,89 %N A385822 Numbers k such that phi(k) is not a perfect square. %e A385822 Since phi(35) = 24 and there is no integer n such that n^2 = 24. %t A385822 Select[Range[100], !IntegerQ[Sqrt[EulerPhi[#]]] &] (* _Amiram Eldar_, Aug 18 2025 *) %o A385822 (Python) %o A385822 from math import isqrt %o A385822 from sympy import totient as phi %o A385822 def ok(n): return isqrt(p:=phi(n))**2 != p %o A385822 print([k for k in range(1, 110) if ok(k)]) # _Michael S. Branicky_, Aug 17 2025 %o A385822 (PARI) isok(k) = !issquare(eulerphi(k)); \\ _Michel Marcus_, Aug 18 2025 %Y A385822 Cf. A000010. Complement of A039770. %K A385822 nonn,easy %O A385822 1,1 %A A385822 _Aidan Chen_, Aug 11 2025