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 A125775 #16 Aug 20 2022 12:00:23
%S A125775 1,2,4,5,6,12,25,42,52,84,125,156,186,372,625,1092,1218,1302,1806,
%T A125775 2436,2604,2756,3125,3612,4836,5334,7212,8268,10668,12324,15625,15918,
%U A125775 18858,19140,20771,24492,26080,31668,31836,33852,37716,37758,40487,41542
%N A125775 Numbers k such that 5^k mod k = 5^k mod k^2.
%C A125775 Includes all powers of 5 (A000351).
%C A125775 a(2) = 2, a(4) = 5, a(35) = 20771 and a(43) = 40487 are the only listed primes. More known primes are listed in A123692.
%H A125775 Amiram Eldar, <a href="/A125775/b125775.txt">Table of n, a(n) for n = 1..1000</a>
%t A125775 Do[f=PowerMod[5,n,n];g=PowerMod[5,n,n^2];If[f==g,Print[n]],{n,1,1000000}]
%t A125775 Select[Range[42000],PowerMod[5,#,#]==PowerMod[5,#,#^2]&] (* _Harvey P. Dale_, Aug 20 2022 *)
%Y A125775 Cf. A000351, A123692, A068535, A125773, A125774.
%K A125775 nonn
%O A125775 1,2
%A A125775 _Alexander Adamchuk_, Dec 07 2006