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A002644
Numbers k such that (k^2 + k + 1)/21 is prime.
(Formerly M5000 N1426)
2
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
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
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[1200], PrimeQ[(#^2 + # + 1)/21] &] (* Vincenzo Librandi, Sep 25 2012 *)
PROG
(PARI) is(n)=isprime((n^2+n+1)/21) \\ Charles R Greathouse IV, Jun 06 2017
CROSSREFS
Sequence in context: A348235 A218439 A192689 * A118489 A110922 A065408
KEYWORD
nonn,easy
EXTENSIONS
More terms from Larry Reeves (larryr(AT)acm.org), Sep 21 2000
STATUS
approved