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 A002642 Numbers n such that (n^2 + n + 1)/13 is prime. (Formerly M4606 N1131) 1
 9, 29, 35, 42, 48, 113, 120, 126, 152, 185, 204, 224, 237, 243, 276, 302, 308, 321, 341, 386, 399, 419, 432, 477, 503, 510, 516, 542, 549, 588, 633, 659, 666, 705, 731, 770, 776, 783, 789, 815, 848, 854, 887, 906, 932, 945, 965, 978 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are congruent to 3 or 9 (mod 13). [Bruno Berselli, Sep 26 2012] 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[1000], PrimeQ[(#^2 + # + 1)/13]&] (* Vincenzo Librandi, Sep 25 2012 *) PROG (PARI) forstep(n=9, 1e4, [7, 6], if(isprime((n^2+n+1)/13), print1(n", "))) \\ Charles R Greathouse IV, Sep 25 2012 (MAGMA) I:=[m: m in [1..1000] | m mod 13 in [3, 9]]; [n: n in I | IsPrime( (n^2 + n + 1) div 13 )]; // Bruno Berselli, Sep 26 2012 CROSSREFS Sequence in context: A024121 A205144 A044976 * A032700 A098949 A031296 Adjacent sequences:  A002639 A002640 A002641 * A002643 A002644 A002645 KEYWORD nonn,easy AUTHOR STATUS approved

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