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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 (list; graph; refs; listen; history; text; internal format)
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

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

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Last modified October 20 22:44 EDT 2019. Contains 328291 sequences. (Running on oeis4.)