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A078683
Least prime of the form n*2^m+1 for m>0, or 0 if there is no such prime.
2
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
N. J. A. Sloane, A Nasty Surprise in a Sequence and Other OEIS Stories, Experimental Mathematics Seminar, Rutgers University, Oct 10 2024, Youtube video; Slides [Mentions this sequence]
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
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Dec 17 2002
EXTENSIONS
Edited by T. D. Noe, Feb 25 2011
STATUS
approved