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 A196499 #19 Jul 04 2021 03:21:39
%S A196499 1,2,3,5,7,9,10,11,13,15,17,19,21,23,25,26,27,29,31,33,34,35,37,39,41,
%T A196499 43,45,47,49,50,51,53,55,57,58,59,61,63,65,67,69,71,73,74,75,77,79,81,
%U A196499 82,83,85,87,89,91,93,95,97,99,101,103,105,106,107,109,111
%N A196499 Numbers k such that the greatest residue of the congruence x^k (mod k) equals k-1 for x in [0..k-1].
%C A196499 All prime numbers are in the sequence.
%H A196499 Amiram Eldar, <a href="/A196499/b196499.txt">Table of n, a(n) for n = 1..10000</a>
%e A196499 50 is in the sequence because the residues of the congruence x^50 (mod 50) are {0, 1, 24, 25, 26, 49} and the greatest value is 50 - 1 = 49.
%t A196499 lst := {}; Do[If[Max[Union[PowerMod[Range[0, n - 1], n, n]]] == n - 1, AppendTo[lst, n]], {n, 120}]; lst
%Y A196499 Cf. A196082.
%K A196499 nonn
%O A196499 1,2
%A A196499 _Michel Lagneau_, Oct 13 2011