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 A002261 Numbers k such that 11*2^k+1 is prime. (Formerly M2425 N0960) 4
 1, 3, 5, 7, 19, 21, 43, 81, 125, 127, 209, 211, 3225, 4543, 10179, 15329, 18759, 28277, 93279, 105741, 268009, 412447, 525589, 644677, 886071, 960901, 1343347, 2230369, 2476839, 2691961, 2897409, 3771821 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES H. Riesel, ``Prime numbers and computer methods for factorization,'' Progress in Mathematics, Vol. 57, Birkhauser, Boston, 1985, Chap. 4, see pp. 381-384. N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS 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 R. M. Robinson, A report on primes of the form k.2^n+1 and on factors of Fermat numbers, Proc. Amer. Math. Soc., 9 (1958), 673-681. MATHEMATICA Select[Range[1000], PrimeQ[11*2^#+1] &] (* Amiram Eldar, Dec 12 2018 *) PROG (PARI) is(n)=ispseudoprime(11*2^n+1) \\ Charles R Greathouse IV, Feb 20 2017 CROSSREFS Sequence in context: A112986 A052333 A074106 * A263257 A261456 A154524 Adjacent sequences:  A002258 A002259 A002260 * A002262 A002263 A002264 KEYWORD hard,nonn AUTHOR EXTENSIONS Added more terms (from http://web.archive.org/web/20161028080239/http://www.prothsearch.net/riesel.html), Joerg Arndt, Apr 07 2013 a(30)-a(32) from http://www.prothsearch.com/riesel1.html by Robert Price, Dec 12 2018 STATUS approved

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Last modified November 29 14:23 EST 2020. Contains 338769 sequences. (Running on oeis4.)