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A002644 Numbers k such that (k^2 + k + 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
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
AUTHOR
EXTENSIONS
More terms from Larry Reeves (larryr(AT)acm.org), Sep 21 2000
STATUS
approved

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Last modified April 23 20:27 EDT 2024. Contains 371916 sequences. (Running on oeis4.)