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A126715
a(n) is the smallest odd prime p such that p*2^n - 1 is prime.
6
3, 3, 3, 3, 3, 7, 3, 3, 5, 7, 5, 3, 5, 31, 5, 79, 17, 7, 3, 61, 17, 7, 83, 13, 83, 61, 11, 193, 83, 7, 521, 43, 5, 31, 3, 31, 17, 31, 3, 61, 107, 19, 53, 3, 557, 7, 23, 31, 5, 19, 11, 1033, 89, 307, 5, 3, 563, 79, 83, 733, 17, 79, 53, 61, 3, 67, 257, 43, 179, 139, 47, 73, 5, 421, 113
OFFSET
0,1
COMMENTS
By Xylouris's version of Linnik's theorem, a(n) << 2^(5.2n). - Charles R Greathouse IV, Dec 28 2011
a(n) = prime(k) for some k < 5*n. - Pierre CAMI, Jul 20 2014
LINKS
Pierre CAMI, Table of n, a(n) for n = 0..10000 (first 2501 terms from T. D. Noe)
MATHEMATICA
f[n_] := Block[{k = 2}, While[ !PrimeQ[ Prime[k]*2^n - 1], k++ ]; Prime@k]; Table[f@n, {n, 0, 74}] (* Robert G. Wilson v, Feb 16 2007 *)
PROG
(PARI) a(n) = p=3; t=2^n; while(!isprime(p*t-1), p=nextprime(p+1)); p \\ Colin Barker, Jul 22 2014
CROSSREFS
Sequence in context: A178154 A270774 A263144 * A158805 A163469 A105121
KEYWORD
nonn
AUTHOR
Pierre CAMI, Feb 13 2007
EXTENSIONS
More terms from Robert G. Wilson v, Feb 16 2007
Entries checked and some errors corrected by N. J. A. Sloane, Mar 02 2007
STATUS
approved