%I A057719
%S A057719 3,19,163,571,1459,8803,9137,17497,41113,52489,78787,87211,135433,
%T A057719 139483,144667,164617,174763,196579,274081,370009,370387,478243,760267,
%U A057719 941489,944803,1041619,1220347,1236787,1319323,1465129,1663579,1994659
%N A057719 Prime factors of numbers in A006521 (numbers n such that n divides 2^n+1).
%C A057719 A prime p is in this sequence iff all prime divisors of ord_p(2)/2 are 
               in this sequence, where ord_p(2) is the order of 2 modulo p. - Max 
               Alekseyev (maxale(AT)gmail.com), Jul 30 2006
%e A057719 2^171+1 = 0 (mod 171), 171=3^3*19 2^13203+1 = 0 (mod 13203), 13203=3^4*163
%o A057719 (PARI) { A057719() = local(S,f); S=Set([2]); forprime(p=3,10^7, f=factorint(znorder(Mod(2,
               p))); if(f[1,1]!=2||f[1,2]!=1,next); f=f[,1]; if(length(setintersect(S,
               Set(f)))==length(f), S=setunion(S,[p]); print1(p,", "))) }
%Y A057719 Cf. A006521, A066364.
%Y A057719 Cf. A136474, A136473.
%Y A057719 Sequence in context: A105784 A077046 A054765 this_sequence A136474 A105624 
               A080835
%Y A057719 Adjacent sequences: A057716 A057717 A057718 this_sequence A057720 A057721 
               A057722
%K A057719 nonn
%O A057719 1,1
%A A057719 Ignacio Larrosa Canestro (ignacio.larrosa(AT)eresmas.net) Oct 26 2000
%E A057719 Edited by Max Alekseyev (maxale(AT)gmail.com) Jul 30 2006