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 A033981 #25 Sep 30 2018 03:13:08 %S A033981 1,5,25,1727,3830879,33554425,19584403931,25086500333,23476467919565, %T A033981 4463061944990945 %N A033981 Integers k such that 2^k == 7 (mod k). %C A033981 A larger term: 15237454403219419167053498809. %t A033981 m = 7; Join[Select[Range[m], Divisible[2^# - m, #] &], %t A033981 Select[Range[m + 1, 10^7], PowerMod[2, #, #] == m &]] (* _Robert Price_, Sep 26 2018 *) %o A033981 (PARI) isok(n) = Mod(2, n)^n == 7; \\ _Michel Marcus_, Sep 27 2018 %K A033981 nonn,more %O A033981 1,2 %A A033981 Joe K. Crump (joecr(AT)carolina.rr.com) %E A033981 Terms 1, 5 prepended by _Max Alekseyev_, May 18 2011 %E A033981 a(9) added by _Max Alekseyev_, May 21 2011 %E A033981 a(10) from _Max Alekseyev_, Jun 17 2012