1,2

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

G. C. Greubel, Table of n, a(n) for n = 1..1000

a(n) = A167692(n)/2.

Select[Range[0, 100], Mod[#, 2] == 0 && !PrimeQ[#] && (! PrimeQ[# - 1] || !PrimeQ[# + 1]) & ]/2 (* G. C. Greubel, Jul 07 2016 *)

Sequence in context: A005048 A119642 A276705 * A248188 A174047 A285085

Adjacent sequences: A168041 A168042 A168043 * A168045 A168046 A168047

nonn,less

Juri-Stepan Gerasimov, Nov 17 2009

approved