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%I #23 Sep 08 2022 08:44:48
%S 3,5,11,15,17,21,27,29,35,39,45,47,53,69,71,75,77,81,83,87,89,95,99,
%T 101,113,119,123,131,141,143,147,153,161,165,167,171,183,185,201,203,
%U 207,209,213,221,225,245,249,251,255,257,263,279,281,285,287,291,297,299,309,311,315
%N Numbers k such that 5*k + 4 is prime.
%H Vincenzo Librandi, <a href="/A024897/b024897.txt">Table of n, a(n) for n = 1..1000</a>
%p A024897:=n->`if`(isprime(5*n+4), n, NULL): seq(A024897(n), n=1..500); # _Wesley Ivan Hurt_, Sep 07 2016
%t Select[Range[400], PrimeQ[5 # + 4]&] (* _Vincenzo Librandi_, Sep 25 2012 *)
%o (Magma) [n: n in [1..1000] | IsPrime(5*n+4)] // _Vincenzo Librandi_, Nov 20 2010
%o (PARI) isok(n) = isprime(5*n+4) \\ _Michel Marcus_, Sep 07 2016
%Y Cf. A023218 (subsequence of primes).
%K nonn,easy
%O 1,1
%A _Clark Kimberling_
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