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A127581 Smallest prime of the form k*2^n - 1, for k >= 2. 17
2, 3, 7, 23, 31, 127, 127, 383, 1279, 3583, 5119, 6143, 8191, 73727, 81919, 131071, 131071, 524287, 524287, 14680063, 14680063, 14680063, 109051903, 109051903, 654311423, 738197503, 738197503, 2147483647, 2147483647, 2147483647 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Table of n, a(n) for n=0..29.

FORMULA

a(n) << 37^n by Xylouris' improvement to Linnik's theorem. - Charles R Greathouse IV, Dec 10 2013

EXAMPLE

a(3)=23 because 23 = 3*2^3 - 1 is prime.

a(4)=31 because 31 = 2*2^4 - 1 is prime.

MATHEMATICA

a = {}; Do[k = 1; While[ !PrimeQ[k 2^n + 2^n - 1], k++ ]; AppendTo[a, k 2^n + 2^n - 1], {n, 0, 50}]; a

CROSSREFS

Cf. A007522, A127575-A127582, A127586-A127587.

Sequence in context: A248346 A236514 A211997 * A278477 A118883 A061712

Adjacent sequences:  A127578 A127579 A127580 * A127582 A127583 A127584

KEYWORD

nonn

AUTHOR

Artur Jasinski, Jan 19 2007

EXTENSIONS

Edited by Don Reble, Jun 11 2007

STATUS

approved

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Last modified April 20 17:54 EDT 2019. Contains 322310 sequences. (Running on oeis4.)