A212311 - OEIS

%I #16 Apr 03 2023 10:36:13

%S 1,15,33,43,61,121,295,315,367,681,771,789,1485,4915,5305,33649,81343,

%T 85005,116307,154869,230731,279591,287847,329515,545353,1053481

%N Numbers n such that 3^8*2^n - 1 is prime.

%C Riesel Primes with k = 3^8 = 6561.

%C Checked up to n = 1053627.

%H K. Bonath,<a href="http://www.rieselprime.de/">Riesel Prime Database</a>

%H C. K. Caldwell, <a href="https://t5k.org/primes/page.php?id=103608">6561*2^1053481-1</a>

%e 6561*2^1-1=13121 is a prime number.

%t b=2^8;i=0; Table[While[i++; cp=b*2^i-1; !PrimeQ[cp]]; i, {j, 1, 13}]

%o (PARI) is(n)=ispseudoprime(3^8*2^n-1) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A002235, A002236, A050539, A050566, A050880, A230527, A230537.

%K nonn,hard

%O 1,2

%A _Lei Zhou_, Oct 24 2013

%E _Lei Zhou_, Nov 08 2013, added a Mathematica program for small elements.