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%I #14 Mar 06 2015 23:03:13
%S 2,7,11,29,19,23,53,31,137,1217,43,47,101,109,59,7937,67,71,149,79,83,
%T 173,181
%N Smallest prime of form (2n+1)*2^m+1 for some m.
%C next term a(23) = 47*2^583+1 > 10^177. Sequence then continues: 197, 103, 107, 881, 229, 1889, 977, 127, 131, 269, 139, 569, 293, 151, 617, 317, 163, 167, 1361, 349, 179, 23297, 373, 191, 389, 199, 809, ...
%C If no such prime exists for any m then 2n+1 is called a Sierpiński number. One could use a(n) = 0 for these cases. E.g., a(39278) = 0 because 78557 is a Sierpiński number. For the corresponding numbers m see A046067(n+1), n >= 0, where -1 entries corresponds to a(n) = 0. See also the Sierpiński links there. - _Wolfdieter Lang_, Feb 07 2013
%H <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 a(5)=23 because 2*5+1=11 and smallest prime of the form 11*2^m+1 is 23 (since 11+1=12 is not prime)
%Y Cf. A032373, A057023, A057026, A046067.
%K nonn
%O 0,1
%A _Henry Bottomley_, Jul 24 2000
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