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 A015940 #14 Sep 22 2016 02:22:31
%S A015940 1,5,917,3223,62911,326329,395819,33504053,4446226763,17556128765,
%T A015940 141613728437,5259417592253,113837290408523
%N A015940 Positive integers n such that 2^n == -3 (mod n).
%C A015940 No other terms below 10^16.
%C A015940 Larger term: 18468744643735483963902321985787. - _Max Alekseyev_, Aug 01 2011
%H A015940 OEIS Wiki, <a href="/wiki/2^n mod n">2^n mod n</a>
%t A015940 Do[ If[ PowerMod[ 2, n, n ] + 3 == n, Print[n]], { n, 1, 10^9, 2 } ]
%Y A015940 Cf. A050259.
%K A015940 nonn,more
%O A015940 1,2
%A A015940 _Robert G. Wilson v_
%E A015940 Corrected and extended by Olivier Wittenberg, May 23 2004.
%E A015940 a(10)-a(13) from _Max Alekseyev_, Aug 01 2011