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%I M5000 N1426 #27 Oct 18 2023 10:04:17
%S 16,25,37,46,58,88,109,130,142,151,184,193,205,247,268,298,310,319,
%T 331,340,382,394,403,415,424,457,478,487,541,550,604,613,688,697,709,
%U 730,739,751,760,793,844,865,886,907,970,1012,1045,1054,1066,1117,1138
%N Numbers k such that (k^2 + k + 1)/21 is prime.
%D A. J. C. Cunningham, Binomial Factorisations, Vols. 1-9, Hodgson, London, 1923-1929; see Vol. 1, pp. 245-259.
%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H Vincenzo Librandi, <a href="/A002644/b002644.txt">Table of n, a(n) for n = 1..1000</a>
%H A. J. C. Cunningham, <a href="/A001912/a001912.pdf">Binomial Factorisations</a>, Vols. 1-9, Hodgson, London, 1923-1929. [Annotated scans of a few pages from Volumes 1 and 2]
%t Select[Range[1200], PrimeQ[(#^2 + # + 1)/21] &] (* _Vincenzo Librandi_, Sep 25 2012 *)
%o (PARI) is(n)=isprime((n^2+n+1)/21) \\ _Charles R Greathouse IV_, Jun 06 2017
%K nonn,easy
%O 1,1
%A _N. J. A. Sloane_
%E More terms from Larry Reeves (larryr(AT)acm.org), Sep 21 2000