A095991 Numbers m such that f(k) * 2^m - 1 is prime, where f(j) = A070826(j) and k is the number of decimal digits of 2^m.

2, 3, 4, 6, 14, 17, 18, 23, 33, 43, 45, 53, 60, 70, 114, 141, 162, 178, 387, 657, 787, 951, 1517, 1882, 1999, 2423, 2722, 3635, 3636, 3893, 5021, 5631, 7580, 7674, 8318, 9479, 19761

Offset: 1

Author

Jason Earls, Jul 18 2004

Keywords

• more
• nonn
• base

Comments

a(1) through a(32) have been proved to be prime with WinPFGW. a(32) has 7901 digits. No more terms up to 7300.

Results were computed using the PrimeFormGW (PFGW) primality-testing program. - Hugo Pfoertner, Nov 14 2019

Examples

			a(5)=14 because 1155 * 2^14 - 1 = 18923519, a prime.
		

Programs

Mathematica

Do[ If[ PrimeQ[ Product[ Prime[i], {i, Floor[ n / Log[2, 10] + 1]}] * 2^(n - 1) - 1], Print[n]], {n, 7300}] (* Robert G. Wilson v, Jul 23 2004 *)

Extensions

Edited by Robert G. Wilson v, Jul 23 2004

a(33)-a(37) from Michael S. Branicky, Aug 03 2024