A057026 Smallest prime of form (2n+1)*2^m-1 for some m, or 0 if no such prime exists.

3, 2, 19, 13, 17, 43, 103, 29, 67, 37, 41, 367, 199, 53, 463, 61, 131, 139, 73, 311, 163, 5503, 89, 751, 97, 101, 211, 109, 113, 241663, 487, 251, 1039, 2143, 137, 283, 9343, 149, 307, 157, 647, 331, 2719, 173, 1423, 181, 743, 379, 193, 197, 103423, 823, 419

Offset

0,1

Comments

If a(329) > 0 it is greater than 659*2^10000. - Robert Israel, Jul 01 2014

Indeed, a(329) > 659*2^100000 if it is nonzero. There does not appear to be a covering set, though, so probably a(329) > 0. - Charles R Greathouse IV, Jul 02 2014

a(329) = 659*2^800516 - 1 (found by David W Linton in 2004). - Robert Israel, Jul 04 2014

Links

Robert Israel, Table of n, a(n) for n = 0..328

Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime

Example

a(5)=43 because 2*5+1=11 and smallest prime of the form 11*2^m-1 is 43 (since 10 and 21 are not prime)

Maple

A057026:= proc(n)
local t;
     t:= 2*n;
     while not isprime(t) do t:= 2*t+1 od;
     t
end proc;
seq(A057026(n), n=0..328); # Robert Israel, Jul 01 2014

Crossrefs

Cf. A057024, A057025, A038699.

Sequence in context: A317927 A075568 A366377 * A032448 A066195 A090587

Adjacent sequences: A057023 A057024 A057025 * A057027 A057028 A057029

Keyword

nonn

Author

Henry Bottomley, Jul 24 2000

Status

approved