A050921 - OEIS

%I #11 Aug 05 2024 18:36:18

%S 2,3,7,5,11,7,29,17,19,11,23,13,53,29,31,17,137,19,1217,41,43,23,47,

%T 97,101,53,109,29,59,31,7937,257,67,137,71,37,149,1217,79,41,83,43,

%U 173,89,181,47

%N Smallest prime of form n*2^m+1, m >= 0, or 0 if no such prime exists.

%C Primes arising from A040076 (or 0 if no such prime exists).

%C Or: Starting with x=n+1, the first prime created by iterating the map x-> 2*x-1. - _Kevin L. Schwartz_ and _Christian N. K. Anderson_, May 13 2013

%H R. J. Mathar, <a href="/A050921/b050921.txt">Table of n, a(n) for n = 1..382</a>

%p A050921 := proc(n)

%p     for m from 0 do

%p         if isprime(n*2^m+1) then

%p             return n*2^m+1 ;

%p         end if;

%p     end do;

%p end proc; # _R. J. Mathar_, Jun 01 2013

%t Do[m = 0; While[ !PrimeQ[n*2^m + 1], m++ ]; Print[n*2^m + 1], {n, 1, 47} ]

%Y Cf. A040076, A034694, A038699.

%K nonn,easy,nice

%O 1,1

%A _N. J. A. Sloane_, Dec 30 1999

%E The next term (47*2^583 + 1) is too large to show.