A002641 Numbers k such that (k^2 + k + 1)/7 is prime. (Formerly M3352 N0446)

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

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 A377466 A106854

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