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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.
0
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
1,1
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
EXAMPLE
a(5)=14 because 1155 * 2^14 - 1 = 18923519, a prime.
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 *)
CROSSREFS
Sequence in context: A188715 A369849 A174046 * A293714 A049911 A056712
KEYWORD
more,nonn,base
AUTHOR
Jason Earls, Jul 18 2004
EXTENSIONS
Edited by Robert G. Wilson v, Jul 23 2004
a(33)-a(37) from Michael S. Branicky, Aug 03 2024
STATUS
approved