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 A366935 #32 Dec 07 2023 21:37:34
%S A366935 3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,25,26,27,28,
%T A366935 29,30,31,32,33,34,35,36,37,38,39,41,42,43,44,45,46,47,49,50,51,52,53,
%U A366935 54,55,57,58,59,61,62,64,66,67,68,69,70,71,73,74,75
%N A366935 Moduli k for which the number of quadratic residues mod k coprime to k is equal to phi(k)/2^(phi(k)/lambda(k)), where lambda is Carmichael's function.
%C A366935 Numbers k such that A046073(k) = A000010(k)/2^A034380(k).
%C A366935 An empirical observation, calculated for 2 <= k <= 10^5. The number of quadratic residues mod k coprime to k is |Q_k| = phi(k)/2^r, r = A046072(k) <= phi(k)/lambda(k). Up to 10^5, the equality holds for 37758 moduli, and the inequality holds for 62241.
%D A366935 D. Shanks, Solved and Unsolved Problems in Number Theory, 4th ed. New York: Chelsea, 1993, page 95.
%H A366935 Miles Englezou, <a href="/A366935/a366935.txt">MATLAB script</a>
%F A366935 { k : |Q_k| = phi(k)/2^(phi(k)/lambda(k)) }, where lambda is Carmichael's function (A002322).
%e A366935 k = 3 is a term: |Q_3| = phi(3)/2^1 = 1, so r = 1 = phi(3)/lambda(3).
%o A366935 (PARI) isok(n) = my(z=znstar(n).cyc); #z == eulerphi(n)/lcm(z) \\ _Andrew Howroyd_, Oct 29 2023
%Y A366935 Cf. A000010, A002322, A046073, A034380, A033948, A046072.
%K A366935 nonn,easy
%O A366935 1,1
%A A366935 _Miles Englezou_, Oct 29 2023