A081765 - OEIS

%I #15 Mar 30 2021 19:43:36

%S 1,7,13,19,31,37,49,55,61,67,85,91,109,121,127,139,157,175,181,193,

%T 199,211,217,235,247,265,289,301,307,313,319,325,337,379,391,397,409,

%U 415,445,451,469,487,499,517,535,541,571,577,589,595,631,667,679,685,691

%N Numbers k such that (k+2) divides 2^(k-1) - 1.

%C Is a(n)/(n*log(n)*log(log(n))) bounded?

%H Amiram Eldar, <a href="/A081765/b081765.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range[1000], PowerMod[2, # - 1, # + 2] == 1 &] (* _Amiram Eldar_, Mar 30 2021 *)

%Y Cf. A000225.

%K easy,nonn

%O 1,2

%A _Benoit Cloitre_, Apr 09 2003