A002732 - OEIS

%I M3281 N1324 #25 Oct 20 2023 09:46:15

%S 4,6,11,14,21,24,26,29,31,39,44,46,51,54,76,79,89,94,99,101,111,119,

%T 124,129,131,136,146,149,154,156,164,176,179,181,194,201,211,214,229,

%U 231,239,244,246,254,261,279,286,294,301,311,314,319,326,331,346,349

%N Numbers k such that (4*k^2 + 1)/5 is prime.

%D L. Euler, De numeris primis valde magnis (E283), reprinted in: Opera Omnia. Teubner, Leipzig, 1911, Series (1), Vol. 3, p. 24.

%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="/A002732/b002732.txt">Table of n, a(n) for n = 1..1000</a>

%H L. Euler, <a href="http://eulerarchive.maa.org/pages/E283.html">De numeris primis valde magnis (E283)</a>, The Euler Archive.

%t Select[Range[0, 400], PrimeQ[(4 #^2 + 1)/5] &] (* _Vincenzo Librandi_, Sep 25 2012 *)

%o (Magma) [n: n in [4..410] | IsPrime((4*n^2+1) div 5)]; // _Vincenzo Librandi_, Sep 25 2012

%o (PARI) is(n)=isprime((4*n^2+1)/5) \\ _Charles R Greathouse IV_, May 22 2017

%K nonn,easy

%O 1,1

%A _N. J. A. Sloane_