A050921 Smallest prime of form n*2^m+1, m >= 0, or 0 if no prime exists.

2, 3, 7, 5, 11, 7, 29, 17, 19, 11, 23, 13, 53, 29, 31, 17, 137, 19, 1217, 41, 43, 23, 47, 97, 101, 53, 109, 29, 59, 31, 7937, 257, 67, 137, 71, 37, 149, 1217, 79, 41, 83, 43, 173, 89, 181, 47

Offset

1,1

Comments

Primes arising from A040076 (or 0 if no such prime exists).

Or: Starting with x=n+1, the first prime created by iterating the map x-> 2*x-1. - Kevin L. Schwartz and Christian N. K. Anderson, May 13 2013

Links

R. J. Mathar, Table of n, a(n) for n = 1..382

Maple

A050921 := proc(n)
    for m from 0 do
        if isprime(n*2^m+1) then
            return n*2^m+1 ;
        end if;
    end do;
end proc; # R. J. Mathar, Jun 01 2013

Mathematica

Do[m = 0; While[ !PrimeQ[n*2^m + 1], m++ ]; Print[n*2^m + 1], {n, 1, 47} ]

Crossrefs

Cf. A040076, A034694, A038699.

Sequence in context: A241082 A219789 A034694 * A087386 A110359 A092977

Adjacent sequences: A050918 A050919 A050920 * A050922 A050923 A050924

Keyword

nonn,easy,nice

Author

N. J. A. Sloane, Dec 30 1999

Extensions

The next term (47*2^583 + 1) is too large to show.

Status

approved