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 A032360 Numbers k such that 21*2^k+1 is prime. 3
 1, 4, 5, 7, 9, 12, 16, 17, 41, 124, 128, 129, 187, 209, 276, 313, 397, 899, 1532, 1613, 1969, 2245, 2733, 4585, 4644, 6712, 6981, 13344, 17524, 27124, 29769, 47337, 55828, 91008, 94801, 164901, 179457, 191337, 200568, 220992, 686632, 856865, 1022168, 1240067 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Jeppe Stig Nielsen, Table of n, a(n) for n = 1..48 Ray Ballinger, Proth Search Page Ray Ballinger and Wilfrid Keller, List of primes k.2^n + 1 for k < 300 Wilfrid Keller, List of primes k.2^n - 1 for k < 300 MATHEMATICA Select[Range[1000], PrimeQ[21*2^#+1] &] (* Amiram Eldar, Dec 12 2018 *) PROG (PARI) is(n)=ispseudoprime(21*2^n+1) \\ Charles R Greathouse IV, Jun 06 2017 (MAGMA) [n: n in [0..5000] | IsPrime(21*2^n+1)]; // Vincenzo Librandi, Dec 12 2018 CROSSREFS Sequence in context: A047493 A285307 A297838 * A117150 A239276 A284132 Adjacent sequences:  A032357 A032358 A032359 * A032361 A032362 A032363 KEYWORD nonn,hard AUTHOR EXTENSIONS More terms from Hugo Pfoertner, Jun 20 2003 Added more terms (from http://web.archive.org/web/20161028080239/http://www.prothsearch.net/riesel.html), Joerg Arndt, Apr 07 2013 a(47) from http://www.prothsearch.com/riesel1.html by Robert Price, Dec 12 2018 Terms moved from Data to b-file, and new term added to b-file, by Jeppe Stig Nielsen, Aug 29 2020 STATUS approved

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Last modified January 21 06:14 EST 2021. Contains 340333 sequences. (Running on oeis4.)