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 A002644 Numbers n such that (n^2 + n + 1)/21 is prime. (Formerly M5000 N1426) 1
 16, 25, 37, 46, 58, 88, 109, 130, 142, 151, 184, 193, 205, 247, 268, 298, 310, 319, 331, 340, 382, 394, 403, 415, 424, 457, 478, 487, 541, 550, 604, 613, 688, 697, 709, 730, 739, 751, 760, 793, 844, 865, 886, 907, 970, 1012, 1045, 1054, 1066, 1117, 1138 (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 MATHEMATICA Select[Range[1200], PrimeQ[(#^2 + # + 1)/21] &] (* Vincenzo Librandi, Sep 25 2012 *) CROSSREFS Sequence in context: A030676 A218439 A192689 * A118489 A110922 A065408 Adjacent sequences:  A002641 A002642 A002643 * A002645 A002646 A002647 KEYWORD nonn,easy AUTHOR EXTENSIONS More terms from Larry Reeves (larryr(AT)acm.org), Sep 21 2000 STATUS approved

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