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 A116638 #19 Apr 10 2020 22:09:59
%S A116638 1,2,158,301823,1851103,8616098,60528467,1087582634,1628818307,
%T A116638 16205558969
%N A116638 Positive integers n such that 13^n == 11 (mod n).
%C A116638 No other terms below 10^15. - _Max Alekseyev_, Nov 07 2018
%C A116638 Large terms: 38763675625170712166, 527929122195463909516681113715859203.
%t A116638 Join[{1, 2}, Select[Range[1, 9000], Mod[13^#, #] == 11 &]] (* _G. C. Greubel_, Nov 20 2017 *)
%t A116638 Join[{1, 2}, Select[Range[10000000], PowerMod[13, #, #] == 11 &]] (* _Robert Price_, Apr 10 2020 *)
%Y A116638 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), A116631 (k=6), A116632 (k=7), A295532 (k=8), A116636 (k=9), A116620 (k=10), this sequence (k=11), A116639 (k=15).
%Y A116638 Cf. A116609.
%K A116638 more,nonn
%O A116638 1,2
%A A116638 _Zak Seidov_, Feb 19 2006
%E A116638 More terms from _Ryan Propper_, Jan 11 2008
%E A116638 Edited by _Max Alekseyev_, May 04 2010