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%I #23 Dec 20 2018 14:03:04
%S 1,5,11,13,65,113,299,335,1235,1991,2861,3295,3343,3901,5545,9125,
%T 10769,14303,19433,28535,76855,206821,207223,530729,1172111,1992071
%N Numbers k such that 209*2^k+1 is prime.
%H Ray Ballinger, <a href="http://www.prothsearch.com/index.html">Proth Search Page</a>
%H Ray Ballinger and Wilfrid Keller, <a href="http://www.prothsearch.com/riesel1.html">List of primes k.2^n + 1 for k < 300</a>
%H Wilfrid Keller, <a href="http://www.prothsearch.com/riesel2.html">List of primes k.2^n - 1 for k < 300</a>
%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>
%t Select[Range[1000], PrimeQ[209*2^# + 1] & ] (* _Robert Price_, Dec 19 2018 *)
%o (PARI) is(n)=ispseudoprime(209*2^n+1) \\ _Charles R Greathouse IV_, Jun 13 2017
%K nonn,hard,more
%O 1,2
%A _N. J. A. Sloane_.
%E a(22)-a(26) from the Ray Ballinger and Wilfrid Keller link by _Robert Price_, Dec 19 2018
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