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A153085 Numbers k such that 4*k + 5 is not prime.

%I A153085 #14 Sep 08 2022 08:45:39
%S A153085 1,4,5,7,10,11,13,15,16,18,19,20,22,25,28,29,30,31,32,34,35,37,39,40,
%T A153085 41,43,45,46,49,50,51,52,53,54,55,58,60,61,62,64,65,67,70,71,73,74,75,
%U A153085 76,79,80,81,82,84,85,88,89,90,91,93,94,95,97,100,102,103,105,106
%N A153085 Numbers k such that 4*k + 5 is not prime.
%C A153085 Let p=2n+1 be an odd number, then A140869(n,n) = (p^2-5)/4 = A028387(n-1).
%C A153085 One less than the associated entry in A045751: a(n) = A045751(n+1)-1. - _R. J. Mathar_, Jan 05 2011
%H A153085 Vincenzo Librandi, <a href="/A153085/b153085.txt">Table of n, a(n) for n = 1..1000</a>
%e A153085 Triangle begins:
%e A153085 1;
%e A153085 *, 5;
%e A153085 4, *, 11;
%e A153085 *, 10, *, 19;
%e A153085 7, *, 18, *, 29;
%e A153085 *, 15, *, 28, *, 41;
%e A153085 where * mark the entries in A140869 which are non-integer if floor(.) is not applied there.
%t A153085 Select[Range[200], !PrimeQ[4 # + 5] &] (* _Vincenzo Librandi_, Oct 15 2012 *)
%o A153085 (Magma) [n: n in [1..120] | not IsPrime(4*n + 5)]; // _Vincenzo Librandi_, Oct 15 2012
%Y A153085 Cf. A028387, A045751, A111215, A140869.
%K A153085 nonn
%O A153085 1,2
%A A153085 _Vincenzo Librandi_, Dec 18 2008