A078683 Least prime of the form n*2^m+1 for m>0, or 0 if there is no such prime.

3, 5, 7, 17, 11, 13, 29, 17, 19, 41, 23, 97, 53, 29, 31, 257, 137, 37, 1217, 41, 43, 89, 47, 97, 101, 53, 109, 113, 59, 61, 7937, 257, 67, 137, 71, 73, 149, 1217, 79, 641, 83, 337, 173, 89, 181, 11777

Offset

1,1

Comments

The next prime has 178 digits. See A078680 for the values of m.

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Mathematica

Table[m=1; While[! PrimeQ[p = n*2^m + 1], m++]; p, {n, 50}]

Prog

(PARI) a(n)=if(n<0, 0, m=1; while(isprime(n*2^m+1)==0, m++); n*2^m+1)

Crossrefs

Cf. A078680.

Sequence in context: A132445 A307437 A070846 * A099863 A112092 A031441

Adjacent sequences: A078680 A078681 A078682 * A078684 A078685 A078686

Keyword

nonn

Author

Benoit Cloitre, Dec 17 2002

Extensions

Edited by T. D. Noe, Feb 25 2011

Status

approved