cp's OEIS Frontend

A238798 Least odd k such that k*2^n + 1 is a prime factor of a Fermat number 2^(2^m) + 1 for some m, or 0 if no such value exists.

%I A238798 #13 Feb 16 2025 08:33:21
%S A238798 0,1,1,0,1,0,0,5,1,116503103764643,0,604944512477,11131,39,7
%N A238798 Least odd k such that k*2^n + 1 is a prime factor of a Fermat number 2^(2^m) + 1 for some m, or 0 if no such value exists.
%C A238798 The sequence continues: a(15) = ?, 1, 17753925353, a(18) = ?, 1575, 13, 579, a(22) = ?
%H A238798 Fermat factoring status, <a href="http://www.prothsearch.com/fermat.html">Prime factors of Fermat numbers</a>
%H A238798 FermatSearch, <a href="http://www.fermatsearch.org/index.html">Home page</a>
%H A238798 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FermatNumber.html">Fermat Number</a>
%Y A238798 Cf. A019434, A007117.
%K A238798 nonn,hard
%O A238798 0,8
%A A238798 _Arkadiusz Wesolowski_, Mar 05 2014