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 A116631 #18 Apr 10 2020 22:10:32
%S A116631 1,7,8743,50239,312389,8789977,87453889,96301009,3963715129,
%T A116631 5062673539,6854133309107,16987071590111,72278468169733,
%U A116631 411419589731633,590475819370933
%N A116631 Positive integers n such that 13^n == 6 (mod n).
%C A116631 No other terms below 10^15. A large term: 2455610470454186971078168169. - _Max Alekseyev_, Dec 19 2017
%t A116631 Join[{1}, Select[Range[1, 9000], Mod[13^#, #] == 6 &]] (* _G. C. Greubel_, Nov 19 2017 *)
%t A116631 Join[{1}, Select[Range[10000000], PowerMod[13, #, #] == 6 &]] (* _Robert Price_, Apr 10 2020 *)
%o A116631 (PARI) isok(n) = Mod(13, n)^n == 6; \\ _Michel Marcus_, Nov 19 2017
%Y A116631 Solutions to 13^n == k (mod n): A001022 (k=0), A015963 (k=-1), A116621 (k=1), A116622 (k=2), A116629 (k=3), A116630 (k=4), A116611 (k=5), this sequence (k=6), A116632 (k=7), A295532 (k=8), A116636 (k=9), A116620(k=10), A116638 (k=11), A116639 (k=15).
%Y A116631 Cf. A116609, A128122, A277628, A277350.
%K A116631 nonn
%O A116631 1,2
%A A116631 _Zak Seidov_, Feb 19 2006
%E A116631 More terms from _Ryan Propper_, Mar 30 2007
%E A116631 Term 1 is prepended and a(11)-a(15) added by _Max Alekseyev_, Jun 29 2011, Dec 19 2017