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 A128123 #20 Jun 13 2021 03:22:52 %S A128123 1,2,6,18,16666,262134,4048124214,24430928839,243293052886, %T A128123 41293676570106,3935632929857549 %N A128123 Numbers k such that 2^k == 10 (mod k). %C A128123 Some larger terms: 266895924489780149, 2335291686841914329, 18494453435532853111 %H A128123 Joe K. Crump, <a href="https://web.archive.org/web/20120104074313/http://www.immortaltheory.com/NumberTheory/2nmodn.htm">2^n mod n</a> %t A128123 m = 10; Join[Select[Range[m], Divisible[2^# - m, #] &], %t A128123 Select[Range[m + 1, 10^6], PowerMod[2, #, #] == m &]] (* _Robert Price_, Oct 08 2018 *) %Y A128123 Cf. A015910, A036236, A050259 (numbers k such that 2^k == 3 (mod k)), A033981, A051447, A033982, A051446, A033983, A128121, A128122, A128124, A128125, A128126. %K A128123 hard,more,nonn %O A128123 1,2 %A A128123 _Alexander Adamchuk_, Feb 15 2007 %E A128123 1, 2 and 6 added by _N. J. A. Sloane_, Apr 23 2007 %E A128123 Missing terms a(9)-a(10) added by _Max Alekseyev_, Dec 16 2013 %E A128123 a(11) from _Max Alekseyev_, Sep 27 2016