cp's OEIS Frontend

A346991 Numbers occurring as divisors of 2^k + 5^k, k > 0.

%I A346991 #11 Dec 09 2022 15:42:19
%S A346991 1,7,11,17,19,23,29,37,41,47,49,53,59,61,73,77,89,97,101,103,109,113,
%T A346991 121,127,131,133,137,139,149,161,167,173,179,181,193,209,211,223,229,
%U A346991 233,241,251,253,257,259,263,269,277,281,287,289,313,317,329,331,337,343
%N A346991 Numbers occurring as divisors of 2^k + 5^k, k > 0.
%C A346991 If k is a term, then so are all divisors of k. - _Robert Israel_, Dec 08 2022
%H A346991 Robert Israel, <a href="/A346991/b346991.txt">Table of n, a(n) for n = 1..10000</a>
%p A346991 filter:= proc(n) local q, v;
%p A346991    if igcd(n,10) <> 1 then return false fi;
%p A346991    q:= 5/2 mod n;
%p A346991    traperror(NumberTheory:-ModularLog(-1,q,n)) <> lasterror
%p A346991 end proc:
%p A346991 filter(1):= true:
%p A346991 select(filter, [$1..400]); # _Robert Israel_, Dec 08 2022
%Y A346991 Cf. A074600, A043292.
%K A346991 nonn
%O A346991 1,2
%A A346991 _Hugo Pfoertner_, Aug 11 2021