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 A124246 #15 Aug 20 2021 04:22:11
%S A124246 1,3,123,202884639,242405133,92273577267,2670733723929,81035221987959
%N A124246 Numbers k that divide 5^k - 2.
%C A124246 No other terms below 10^15. Some larger terms: 60092749466423900486673922957841, 401021769827858799355246286337987697472836927856337282726789534497163. - _Max Alekseyev_, Oct 15 2016
%t A124246 Do[If[Mod[(PowerMod[5,n,n]-2),n]==0,Print[n]],{n,1000000000}]
%o A124246 (PARI) is(n)=Mod(5,n)^n==2 \\ _Charles R Greathouse IV_, Nov 04 2016
%Y A124246 Solutions to 5^n == k (mod n): A067946 (k=1), A015951 (k=-1), this sequence (k=2), A123062 (k=-2), A123061 (k=3), A123052 (k=-3), A125949 (k=4), A123047 (k=-4), A123091 (k=5), A015891 (k=-5), A277350 (k=6), A277348 (k=-6).
%K A124246 nonn
%O A124246 1,2
%A A124246 _Farideh Firoozbakht_, Nov 19 2006
%E A124246 a(6)-a(8) from _Max Alekseyev_, Jul 28 2009, Jun 02 2010, Oct 15 2016