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 A002254 Numbers k such that 5*2^k + 1 is prime. (Formerly M2635 N1046) 12
 1, 3, 7, 13, 15, 25, 39, 55, 75, 85, 127, 1947, 3313, 4687, 5947, 13165, 23473, 26607, 125413, 209787, 240937, 819739, 1282755, 1320487, 1777515 (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 C. K. Caldwell, The Prime Pages 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. 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. [Annotated scanned copy of selected pages. The first page is (accidentally) included with the scan of the Wilson letter below.] Eric Weisstein's World of Mathematics, Proth Prime MATHEMATICA lst={}; Do[If[PrimeQ[5*2^n+1], AppendTo[lst, n]], {n, 0, 2*10^3}]; lst (* Vladimir Joseph Stephan Orlovsky, Aug 19 2008 *) PROG (PARI) is(n)=isprime(5*2^n+1) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Cf. A050526. Sequence in context: A255682 A080565 A164344 * A060657 A192148 A151875 Adjacent sequences:  A002251 A002252 A002253 * A002255 A002256 A002257 KEYWORD hard,more,nonn AUTHOR EXTENSIONS Corrected (removed incorrect term 40937) and added more terms (from http://web.archive.org/web/20161028080239/http://www.prothsearch.net/riesel.html), Joerg Arndt, Apr 07 2013 STATUS approved

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Last modified August 22 20:47 EDT 2019. Contains 326209 sequences. (Running on oeis4.)