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A138576 Numbers n such that 2^(2*n-1)-1 is prime. 1
2, 3, 4, 7, 9, 10, 16, 31, 45, 54, 64, 261, 304, 640, 1102, 1141, 1609, 2127, 2212, 4845, 4971, 5607, 9969, 10851, 11605, 22249, 43122, 55252, 66025, 108046, 378420, 429717, 628894, 699135, 1488111, 1510689, 3486297, 6733459, 10498006 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..39.

FORMULA

a(n) = (A000043(n+1)+1)/2

EXAMPLE

2^(2*2-1)-1=7, 2^(2*3-1)-1=31, 2^(2*4-1)-1=127,...

MATHEMATICA

For[i=1, i<=1, a={}; Do[x=2^(2*n-i)-i; If[PrimeQ[x], AppendTo[a, n]], {n, 10^2}]; Print["2^(2*n-", i, "), ", a]; i=i+2]

PROG

(PARI) is(n)=isprime(2^(2*n-1)-1) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Sequence in context: A141748 A057267 A277066 * A259483 A187503 A038197

Adjacent sequences:  A138573 A138574 A138575 * A138577 A138578 A138579

KEYWORD

nonn,easy

AUTHOR

Vladimir Joseph Stephan Orlovsky, May 13 2008

EXTENSIONS

Formula and more terms from Charles R Greathouse IV, Aug 30 2010

STATUS

approved

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Last modified January 25 17:16 EST 2020. Contains 331245 sequences. (Running on oeis4.)