%I #21 Dec 20 2018 14:03:04

%S 279,415,711,115807,241071

%N Numbers n such that 257*2^n+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>

%o (PARI) is(n)=ispseudoprime(257*2^n+1) \\ _Charles R Greathouse IV_, Jun 07 2017

%K nonn,hard

%O 1,1

%A _N. J. A. Sloane_.

%E One more term (from the Ballinger-Keller web page) from _M. F. Hasler_, Apr 18 2007