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%I #15 Feb 23 2021 15:07:10
%S 0,4,5,7,8,10,11,12,13,14,16,17,18,19,20,22,23,24,25,26,27,28,29,31,
%T 32,33,34,35,37,38,39,40,41,42,43,44,45,46,47,48,49,50,52,53,55,56,57,
%U 58,59,60,61,62,63,64,65,66,67,68,70,71,72,73,74,76,77,78,79,80,81,82,83
%N Half of the even nonisolated nonprimes A167692.
%C Apart from the first term, numbers n with at least one of 2n-1 and 2n+1 composite. - _Charles R Greathouse IV_, Mar 25 2010
%C It is possible to create a sieve for twin primes because these numbers are of the form i+j+2*i*j and 1+i+j+2*i*j for i,j >= 1. Except 1, complement of A040040 where 2*a(n)-1 and 2*a(n)+1 are twin primes. - _Davide Rotondo_, Jan 19 2021
%H G. C. Greubel, <a href="/A168044/b168044.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = A167692(n)/2.
%t Select[Range[0,100], Mod[#, 2] == 0 && !PrimeQ[#] && (! PrimeQ[# - 1] || !PrimeQ[# + 1]) & ]/2 (* _G. C. Greubel_, Jul 07 2016 *)
%Y Cf. A167692.
%Y Except 1, complement of A040040.
%K nonn,less
%O 1,2
%A _Juri-Stepan Gerasimov_, Nov 17 2009
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