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 A015931 #21 Apr 01 2017 09:02:17 %S A015931 1,2,3,4,5,8,9,16,17,21,27,32,45,63,64,99,105,117,124,128,153,171,189, %T A015931 207,254,256,261,273,279,333,369,387,423,429,477,512,513,531,549,585, %U A015931 603,639,657,711,747,801,873,909,927,945,963,981,1017,1143,1179,1197,1209,1233,1251,1341,1359,1365,1413,1467,1472,1503,1504,1557,1611,1629,1665,1719,1737,1773,1785,1791,1899,1971 %N A015931 Positive integers n such that 2^n (mod n) == 2^9 (mod n). %C A015931 For all m, 2^A128123(m)-1 belongs to this sequence. %H A015931 Seiichi Manyama, <a href="/A015931/b015931.txt">Table of n, a(n) for n = 1..10000</a> %H A015931 OEIS Wiki, <a href="/wiki/2^n mod n">2^n mod n</a> %t A015931 Select[Range[2000],PowerMod[2,9,#]==PowerMod[2,#,#]&] (* _Harvey P. Dale_, Apr 01 2017 *) %o A015931 (PARI) isok(n) = Mod(2, n)^n == 2^9; \\ _Michel Marcus_, Sep 23 2016 %Y A015931 Contains A208157 as a subsequence. %Y A015931 The odd terms form A276970. %K A015931 nonn %O A015931 1,2 %A A015931 _Robert G. Wilson v_ %E A015931 Edited by _Max Alekseyev_, Jul 30 2011 %E A015931 Definition clarified by _Harvey P. Dale_, Apr 01 2017