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
Keywords
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..1000
- 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]
Crossrefs
Cf. A078680.
Programs
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Mathematica
Table[m=1; While[! PrimeQ[p = n*2^m + 1], m++]; p, {n, 50}] -
PARI
a(n)=if(n<0, 0, m=1; while(isprime(n*2^m+1)==0, m++); n*2^m+1)
Extensions
Edited by T. D. Noe, Feb 25 2011
Comments