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A110994 Numbers n such that 23*n^2 - 4 is prime. 1

%I #12 Jul 04 2018 01:57:12

%S 1,5,7,15,21,23,27,49,63,65,83,89,103,107,131,135,149,159,161,181,187,

%T 197,203,209,223,231,237,245,253,257,261,279,281,301,307,313,327,331,

%U 335,337,369,371,377,385,397

%N Numbers n such that 23*n^2 - 4 is prime.

%H Robert Israel, <a href="/A110994/b110994.txt">Table of n, a(n) for n = 1..10000</a>

%e If n=89 then 23*n^2 - 4 = 182179 (prime).

%p select(n -> isprime(23*n^2-4), [seq(i,i=1..1000,2)]); # _Robert Israel_, Jul 04 2018

%t Select[Range[400], PrimeQ[(23#^2 - 4)] &] (* _Stefan Steinerberger_, Feb 28 2006 *)

%o (PARI) is(n)=isprime(23*n^2-4) \\ _Charles R Greathouse IV_, Jun 13 2017

%K nonn,easy

%O 1,2

%A _Parthasarathy Nambi_, Sep 30 2005

%E More terms from _Stefan Steinerberger_, Feb 28 2006

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Last modified June 12 13:39 EDT 2024. Contains 373331 sequences. (Running on oeis4.)