%I #41 Aug 16 2021 03:12:38

%S 1,3,15,75,6308237,871506915,2465425275,2937864075,2948967789,

%T 83313712623,195392257275,11126651718075,45237726869109,

%U 2920008144904215

%N Numbers k that divide 2^k + 7.

%C Some larger terms: 213736983815110866141, 23423890178454972202084722709155. - _Max Alekseyev_, Sep 23 2016

%H OEIS Wiki, <a href="/wiki/2^n mod n">2^n mod n</a>

%e 2^3 + 7 = 15 is divisible by 3. Thus 3 is a term of this sequence.

%t k = 1; lst = {1,3}; While[k < 2500000001, If[ PowerMod[2, k, k] + 7 == k, AppendTo[ lst, k]; Print[ k]]; k += 2]; lst (* _Robert G. Wilson v_, Aug 05 2014 *)

%o (PARI)

%o for(n=1,10^9,if(Mod(2,n)^n==Mod(-7,n),print1(n,", ")))

%Y Cf. A033981, A168415.

%K nonn,more,hard

%O 1,2

%A _Derek Orr_, Aug 04 2014

%E a(7)-a(9) from _Robert G. Wilson v_, Aug 05 2014

%E a(10)-a(14) from _Max Alekseyev_, Sep 23 2016