A161539 - OEIS

%I #8 Nov 21 2013 12:49:38

%S 2,5,6,7,9,10,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,28,30,31,

%T 32,33,34,35,36,37,38,39,41,42,43,46,48,49,50,51,52,53,54,55,56,59,60,

%U 61,62,63,64,65,67,68,70,72,73,74,75,76,77,78,79,80,81,82,85,86,87,88,89

%N Numbers n such that composite (n) + n is a composite, where composite (n) denotes the n-th composite number.

%C 2 is in the list because composite(2)+2 =6+2 = 8 and 8 is composite.

%C 5 is in the list because composite(5)+5 =10+5 = 15 and 15 is composite.

%t With[{comps=Complement[Range[2,250],Prime[Range[PrimePi[250]]]]}, Transpose[Select[Thread[{Range[Length[comps]],comps}],!PrimeQ[ Total[#]]&]][[1]]] (* _Harvey P. Dale_, Dec 02 2011 *)

%Y Cf. A002808.

%Y Complement of A161538.

%K nonn

%O 1,1

%A _Claudio Meller_, Jun 13 2009