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 A036260 #12 Jul 30 2020 03:58:57 %S A036260 2921,3017,3473,3479,5767,5969,6167,6377,6497,6913,7223,7519,7567, %T A036260 7751,9017,9271,10199,10447,11431,11929,12719,13439,13609,14513,16583, %U A036260 17009,17143,18631,18809,19313,20737,21119,22337,22351,22537 %N A036260 Numbers k > 1 such that k mod ord2(k) is even, where ord2(k) is the order of 2 mod k. %C A036260 These are all composite since for prime p, ord2(p) | phi(p) = p-1, whence p mod ord2(p) = 1. %H A036260 Amiram Eldar, <a href="/A036260/b036260.txt">Table of n, a(n) for n = 1..10000</a> %t A036260 Select[Range[3, 23000, 2], EvenQ[Mod[#, MultiplicativeOrder[2, #]]] &] (* _Amiram Eldar_, Jul 30 2020 *) %Y A036260 Cf. A002326, A007733, A036259. %K A036260 nonn %O A036260 1,1 %A A036260 _David W. Wilson_ %E A036260 Offset corrected by _Amiram Eldar_, Jul 30 2020