A153308 - OEIS

%I #11 Sep 08 2022 08:45:39

%S 2,5,7,8,11,14,17,18,20,21,23,24,26,28,29,32,35,37,38,40,41,42,43,44,

%T 47,49,50,51,52,53,56,59,62,63,65,66,68,69,70,71,73,74,76,77,80,81,83,

%U 84,86,89,91,92,95,98,100,101,102,103,104,105,106,107

%N Numbers n such that 10*n+7 is not prime.

%H Vincenzo Librandi, <a href="/A153308/b153308.txt">Table of n, a(n) for n = 1..1000</a>

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

%e *;

%e *,*;

%e *,*,*;

%e 2,*,*,*;

%e *,*,7,*,*;

%e *,*,*,11,*,*;

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

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

%e 5,*,*,*,*,24,*,*,*;

%e *,*,14,*,*,*,*,35,*,*;

%e *,*,*,20,*,*,*,*,43,*,*;etc.

%e where * marks the non-integer values of (2*h*k + k + h - 3)/5 with h >= k >= 1. - _Vincenzo Librandi_, Jan 17 2013

%t Select[Range[0, 200], !PrimeQ[10*# + 7]&] (* _Vincenzo Librandi_, Jan 12 2013 *)

%o (Magma) [n: n in [0..150] | not IsPrime(10*n + 7)]; // _Vincenzo Librandi_, Jan 12 2013

%Y A102342.

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Dec 23 2008