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 A081765 #15 Mar 30 2021 19:43:36 %S A081765 1,7,13,19,31,37,49,55,61,67,85,91,109,121,127,139,157,175,181,193, %T A081765 199,211,217,235,247,265,289,301,307,313,319,325,337,379,391,397,409, %U A081765 415,445,451,469,487,499,517,535,541,571,577,589,595,631,667,679,685,691 %N A081765 Numbers k such that (k+2) divides 2^(k-1) - 1. %C A081765 Is a(n)/(n*log(n)*log(log(n))) bounded? %H A081765 Amiram Eldar, <a href="/A081765/b081765.txt">Table of n, a(n) for n = 1..10000</a> %t A081765 Select[Range[1000], PowerMod[2, # - 1, # + 2] == 1 &] (* _Amiram Eldar_, Mar 30 2021 *) %Y A081765 Cf. A000225. %K A081765 easy,nonn %O A081765 1,2 %A A081765 _Benoit Cloitre_, Apr 09 2003