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A057026 Smallest prime of form (2n+1)*2^m-1 for some m, or 0 if no such prime exists.

%I A057026 #15 Jul 04 2014 18:29:53
%S A057026 3,2,19,13,17,43,103,29,67,37,41,367,199,53,463,61,131,139,73,311,163,
%T A057026 5503,89,751,97,101,211,109,113,241663,487,251,1039,2143,137,283,9343,
%U A057026 149,307,157,647,331,2719,173,1423,181,743,379,193,197,103423,823,419
%N A057026 Smallest prime of form (2n+1)*2^m-1 for some m, or 0 if no such prime exists.
%C A057026 If a(329) > 0 it is greater than 659*2^10000. - _Robert Israel_, Jul 01 2014
%C A057026 Indeed, a(329) > 659*2^100000 if it is nonzero. There does not appear to be a covering set, though, so probably a(329) > 0. - _Charles R Greathouse IV_, Jul 02 2014
%C A057026 a(329) = 659*2^800516 - 1 (found by David W Linton in 2004). - _Robert Israel_, Jul 04 2014
%H A057026 Robert Israel, <a href="/A057026/b057026.txt">Table of n, a(n) for n = 0..328</a>
%H A057026 <a href="/index/Pri#riesel">Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime</a>
%e A057026 a(5)=43 because 2*5+1=11 and smallest prime of the form 11*2^m-1 is 43 (since 10 and 21 are not prime)
%p A057026 A057026:= proc(n)
%p A057026 local t;
%p A057026      t:= 2*n;
%p A057026      while not isprime(t) do t:= 2*t+1 od;
%p A057026      t
%p A057026 end proc;
%p A057026 seq(A057026(n),n=0..328); # _Robert Israel_, Jul 01 2014
%Y A057026 Cf. A057024, A057025, A038699.
%K A057026 nonn
%O A057026 0,1
%A A057026 _Henry Bottomley_, Jul 24 2000