A153381 - OEIS

%I #15 Sep 08 2022 08:45:39

%S 1,2,3,4,5,7,8,9,10,11,13,14,15,17,18,19,20,21,22,23,25,26,27,29,30,

%T 31,32,33,35,37,38,39,40,41,43,44,45,46,47,48,49,50,51,53,55,56,57,59,

%U 60,61,62,63,65,66,67,68,69,70,71,73,74,75,76,77,79,80,81,83,85,86,87,88

%N Numbers n such that 11*n+5 is not prime.

%H Vincenzo Librandi, <a href="/A153381/b153381.txt">Table of n, a(n) for n = 1..1000</a>

%e Distribution of the even terms in the following triangular array:

%e *;

%e *,*;

%e *,*,4;

%e 2,*,*,*;

%e *,*,*,*,*;

%e *,*,*,*,*,*;

%e *,*,*,*,*,*,20;

%e *,*,*,*,*,*,*,*,;

%e *,*,*,*,*,22,*,*,*;

%e *,*,*,*,*,*,*,32,*,*;

%e *,10,*,*,*,*,*,*,*,*,*;

%e *,*,*,20,*,*,*,*,*,*,*,*;

%e *,*,*,*,*,*,*,*,*,*,56,*,*:

%e *,*,18,*,*,*,*,*,*,*,*,*,*,76;

%e 8,*,*,*,*,*,*,*,*,*,*,70,*,*,*; etc.

%e where * marks the non-integer values of (4*h*k + 2*k + 2*h - 4)/11 with h >= k >= 1. - _Vincenzo Librandi_, Jan 17 2013

%t Select[Range[0, 200], !PrimeQ[11 # + 5] &] (* _Vincenzo Librandi_, Jan 13 2013 *)

%o (Magma) [n: n in [0..150] | not IsPrime(11*n+5)]; // _Vincenzo Librandi_, Jan 13 2013

%Y Cf. A108233.

%K nonn,easy

%O 1,2

%A _Vincenzo Librandi_, Dec 25 2008

%E Erroneous comment deleted by _N. J. A. Sloane_, Jun 23 2010