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 A002641 Numbers k such that (k^2 + k + 1)/7 is prime. (Formerly M3352 N0446) 3
 4, 9, 11, 23, 32, 39, 44, 51, 53, 60, 65, 72, 86, 93, 95, 114, 123, 156, 170, 179, 186, 200, 207, 212, 219, 228, 233, 240, 249, 261, 270, 303, 317, 333, 338, 345, 375, 389, 401, 443, 452, 473, 480, 492, 515, 534, 548, 564, 578, 585, 597, 599, 611, 641, 660, 662 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES A. J. C. Cunningham, Binomial Factorisations, Vols. 1-9, Hodgson, London, 1923-1929; see Vol. 1, pp. 245-259. 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 Vincenzo Librandi, Table of n, a(n) for n = 1..1000 A. J. C. Cunningham, Binomial Factorisations, Vols. 1-9, Hodgson, London, 1923-1929. [Annotated scans of a few pages from Volumes 1 and 2] MATHEMATICA Select[Range[700], PrimeQ[(#^2 + # + 1)/7] &] (* Harvey P. Dale, Sep 16 2011 *) PROG (Magma) /* See Crossrefs: */ A047348:=[m: m in [1..700] | m mod 7 in [2, 4]]; [n: n in A047348 | IsPrime( (n^2+n+1) div 7 )]; // Bruno Berselli, Sep 26 2012 (PARI) is(n)=isprime((n^2+n+1)/7) \\ Charles R Greathouse IV, May 22 2017 CROSSREFS Subsequence of A047348. Sequence in context: A141365 A179055 A277428 * A085724 A106854 A099458 Adjacent sequences: A002638 A002639 A002640 * A002642 A002643 A002644 KEYWORD nonn,easy AUTHOR N. J. A. Sloane EXTENSIONS More terms from Jon E. Schoenfield, Mar 24 2010 STATUS approved

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Last modified September 10 09:32 EDT 2024. Contains 375786 sequences. (Running on oeis4.)