A212311 Numbers n such that 3^8*2^n - 1 is prime.

1, 15, 33, 43, 61, 121, 295, 315, 367, 681, 771, 789, 1485, 4915, 5305, 33649, 81343, 85005, 116307, 154869, 230731, 279591, 287847, 329515, 545353, 1053481

Offset

1,2

Comments

Riesel Primes with k = 3^8 = 6561.

Checked up to n = 1053627.

Links

Table of n, a(n) for n=1..26.

K. Bonath,Riesel Prime Database

C. K. Caldwell, 6561*2^1053481-1

Example

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

Mathematica

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

Prog

(PARI) is(n)=ispseudoprime(3^8*2^n-1) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

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

Sequence in context: A162887 A231370 A246755 * A262741 A351562 A316153

Adjacent sequences: A212308 A212309 A212310 * A212312 A212313 A212314

Keyword

nonn,hard

Author

Lei Zhou, Oct 24 2013

Extensions

Lei Zhou, Nov 08 2013, added a Mathematica program for small elements.

Status

approved