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Numbers n > 1 such that 2*n-3 is not a prime.
8

%I #27 Sep 08 2022 08:45:39

%S 2,6,9,12,14,15,18,19,21,24,26,27,29,30,33,34,36,39,40,42,44,45,47,48,

%T 49,51,54,57,59,60,61,62,63,64,66,68,69,72,73,74,75,78,79,81,82,84,86,

%U 87,89,90,93,94,95,96,99,102,103,104,105,106,108,109,110

%N Numbers n > 1 such that 2*n-3 is not a prime.

%C One more than the associated value in A104275. - _R. J. Mathar_, Jan 05 2011

%C 2*A155705(m,n)-3 = (2n+1)*(2m+1) are nonprime: all A155705(.,.) are in this sequence.

%C The terms after a(1) are the values of 2*h*k + k + h + 2, where h and k are positive integers. - _Vincenzo Librandi_, Jan 19 2013

%H Vincenzo Librandi, <a href="/A153043/b153043.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[2,200], !PrimeQ[2*#-3]&] (* _Vladimir Joseph Stephan Orlovsky_, Feb 09 2012 *)

%o (Magma) [n: n in [2..102] | not IsPrime(2*n-3)]; // _Bruno Berselli_, Mar 05 2011

%Y Cf. A098090, A104275, A153040, A155705.

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Dec 17 2008