This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A127582 a(n) = the smallest prime number of the form k*2^n - 1, for k >= 1. 3
 2, 3, 3, 7, 31, 31, 127, 127, 1279, 3583, 5119, 6143, 8191, 8191, 81919, 131071, 131071, 131071, 524287, 524287, 14680063, 14680063, 109051903, 109051903, 654311423, 738197503, 738197503, 2147483647, 2147483647, 2147483647 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Robert Israel, Table of n, a(n) for n = 0..3310 FORMULA a(n) << 37^n by Xylouris's improvement to Linnik's theorem. - Charles R Greathouse IV, Dec 10 2013 EXAMPLE a(0)=2 because 2 = 3*2^0 - 1 is prime. a(1)=3 because 3 = 2*2^1 - 1 is prime. a(2)=3 because 3 = 1*2^2 - 1 is prime. a(3)=7 because 7 = 1*2^3 - 1 is prime. a(4)=31 because 31 = 2*2^4 - 1 is prime. MAPLE p:= 2: A[0]:= 2: for n from 1 to 100 do   if p+1 mod 2^n = 0 then A[n]:= p   else     p:=p+2^(n-1);     while not isprime(p) do p:= p+2^n od:     A[n]:= p;   fi od: seq(A[i], i=0..100); # Robert Israel, Jan 13 2017 MATHEMATICA a = {}; Do[k = 0; While[ !PrimeQ[k 2^n + 2^n - 1], k++ ]; AppendTo[a, k 2^n + 2^n - 1], {n, 0, 50}]; a - Artur Jasinski, Jan 19 2007 CROSSREFS Cf. A007522, A127575-A127581, A127583-A127587. A087522 is identical except for a(1). Sequence in context: A176022 A316275 A113031 * A157144 A096714 A078035 Adjacent sequences:  A127579 A127580 A127581 * A127583 A127584 A127585 KEYWORD nonn AUTHOR Artur Jasinski, Jan 19 2007 EXTENSIONS Edited by Don Reble, Jun 11 2007 Further edited by N. J. A. Sloane, Jul 03 2008 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 19 06:57 EDT 2019. Contains 323386 sequences. (Running on oeis4.)