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A153049 Numbers n such that 2*n - 13 is not a prime.

%I A153049 #16 Sep 08 2022 08:45:39
%S A153049 7,11,14,17,19,20,23,24,26,29,31,32,34,35,38,39,41,44,45,47,49,50,52,
%T A153049 53,54,56,59,62,64,65,66,67,68,69,71,73,74,77,78,79,80,83,84,86,87,89,
%U A153049 91,92,94,95,98,99,100,101,104,107,108,109,110,111,113,114,115,116
%N A153049 Numbers n such that 2*n - 13 is not a prime.
%C A153049 All entries of A163672 are in the sequence because 2*A163672(n,m)-13 = (2n+1)(2m+1) is not prime.  - _R. J. Mathar_, Jan 05 2011
%H A153049 Vincenzo Librandi, <a href="/A153049/b153049.txt">Table of n, a(n) for n = 1..1000</a>
%e A153049 Distribution of a(n) > 7 in the following triangular array:
%e A153049 11;
%e A153049 14,19;
%e A153049 17,24,31;
%e A153049 20,29,38,47;
%e A153049 23,34,45,56,67;
%e A153049 26,39,52,65,78,91;
%e A153049 29,44,59,74,89,104,119;
%e A153049 32,49,66,83,100,117,134,151;
%e A153049 35,54,73,92,111,130,149,168,187;
%e A153049 38,59,80,101,122,143,164,185,206,227;
%e A153049 41,64,87,110,133,156,179,202,225,248,271;
%e A153049 44,69,94,119,144,169,194,219,244,269,294,319; etc.
%e A153049 which is obtained by (2*h*k + k + h + 7) with h >= k >= 1. - _Vincenzo Librandi_, Jan 15 2013
%t A153049 Select[Range[7, 200],!PrimeQ[2 # - 13] &] (* _Vincenzo Librandi_, Oct 15 2012 *)
%o A153049 (Magma) [n: n in [7..120] | not IsPrime(2*n - 13)]; // _Vincenzo Librandi_, Oct 15 2012
%Y A153049 Cf. A097363, A163672.
%K A153049 nonn,easy
%O A153049 1,1
%A A153049 _Vincenzo Librandi_, Dec 17 2008