A050880 - OEIS

%I #29 Dec 20 2018 14:03:04

%S 2,6,8,11,12,18,24,27,36,38,44,56,58,62,116,134,162,242,274,348,358,

%T 478,512,548,658,824,1242,1287,1531,2846,3343,4818,4856,5051,6024,

%U 7431,7434,9432,9667,13059,13482,18111,19004,33571,40174,41467,53206,57978,61438

%N Numbers n such that 243*2^n-1 is prime.

%H Lei Zhou, <a href="/A050880/b050880.txt">Table of n, a(n) for n = 1..67</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 L. Soule and K. Bonath, <a href="http://www.rieselprime.de/">Riesel Prime database</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 b=3^5; i=0; Table[While[i++; cp=b*2^i-1; !PrimeQ[cp]]; i, {j, 1, 33}] (* _Lei Zhou_, Nov 08 2013 *)

%o (PARI) is(n)=ispseudoprime(243*2^n-1) \\ _Charles R Greathouse IV_, Feb 20 2017

%K hard,nonn

%O 1,1

%A _N. J. A. Sloane_, Dec 29 1999

%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008