%I #21 Mar 13 2023 07:19:36
%S 3,5,7,17,11,13,29,17,19,41,23,97,53,29,31,257,137,37,1217,41,43,89,
%T 47,97,101,53,109,113,59,61,7937,257,67,137,71,73,149,1217,79,641,83,
%U 337,173,89,181,11777
%N Least prime of the form n*2^m+1 for m>0, or 0 if there is no such prime.
%C The next prime has 178 digits. See A078680 for the values of m.
%H Vincenzo Librandi, <a href="/A078683/b078683.txt">Table of n, a(n) for n = 1..1000</a>
%t Table[m=1; While[! PrimeQ[p = n*2^m + 1], m++]; p, {n, 50}]
%o (PARI) a(n)=if(n<0, 0, m=1; while(isprime(n*2^m+1)==0, m++); n*2^m+1)
%Y Cf. A078680.
%K nonn
%O 1,1
%A _Benoit Cloitre_, Dec 17 2002
%E Edited by _T. D. Noe_, Feb 25 2011
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