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A138576 Numbers k such that 2^(2*k - 1) - 1 is prime. 2
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, 12018292, 12982476, 15201229, 16291329, 18578334 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = (A000043(n+1) + 1)/2. - Charles R Greathouse IV, Aug 30 2010
a(n) = A146768(n) + 1. - César Aguilera, May 27 2020
EXAMPLE
2^(2*2 - 1) - 1 = 7;
2^(2*3 - 1) - 1 = 31;
2^(2*4 - 1) - 1 = 127.
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
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
More terms from Charles R Greathouse IV, Aug 30 2010
More terms from Mario García, Jul 18 2022
STATUS
approved

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Last modified April 21 17:36 EDT 2024. Contains 371874 sequences. (Running on oeis4.)