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 A015973 #17 Oct 14 2016 17:20:28 %S A015973 1,5,77,278377,3697489,219596687717,56865169816619 %N A015973 Positive integers n such that n | (3^n + 2). %C A015973 No other terms below 10^15. Some larger term: 3142423971953435020522506484187. - _Max Alekseyev_, Aug 04 2011 %Y A015973 Cf. A015940, A050259, A123062 %Y A015973 Solutions to 3^n == k (mod n): A277340 (k=-11), A277289 (k=-7), A277288 (k=-5), this sequence (k=-2), A015949 (k=-1), A067945 (k=1), A276671 (k=2), A276740 (k=5), A277126 (k=7), A277274 (k=11). %K A015973 nonn,more %O A015973 1,2 %A A015973 _Robert G. Wilson v_ %E A015973 a(1)=1 prepended and a(6)-a(7) added by _Max Alekseyev_, Aug 04 2011