|
%I #27 Mar 20 2023 13:06:24
%S 6,11,13,24,26,27,31,34,36,41,46,48,56,57,62,63,69,71,73,88,91,92,96,
%T 97,101,102,104,106,111,116,119,122,123,126,132,136,139,154,166,167,
%U 171,173,174,176,178,179,187,188,189,193,196,201,206,207,209,216,221
%N Numbers k such that 6*k-1 is composite, but 6*k-5 is prime.
%H Vincenzo Librandi, <a href="/A199717/b199717.txt">Table of n, a(n) for n = 1..1000</a>
%t Select[Range[221], PrimeQ[6 # - 5] && ! PrimeQ[6 # - 1] &] (* _T. D. Noe_, Nov 09 2011 *)
%o (Magma) [ p div 6 +1: p in PrimesUpTo(1326) | not IsPrime(p+4) and p mod 6 eq 1 ]; // _Bruno Berselli_, Nov 09 2011
%o (PARI) is(n)=isprime(6*n-5) && !isprime(6*n-1) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A186243.
%K nonn,easy
%O 1,1
%A _Eleonora Echeverri-Toro_, Nov 09 2011
|
