A210999 - OEIS

%I #13 Oct 08 2012 21:36:55

%S 6,12,18,24,25,26,27,28,32,33,34,35,36,42,48,49,50,51,52,60,68,69,70,

%T 74,75,76,77,78,84,85,86,87,88,98,99,100,104,105,106,110,111,112,128,

%U 129,130,138,150,158,159,160,161,162,168,169,170,171,172

%N Composite numbers that are in the gap between an odd-indexed prime and an even-indexed prime.

%H Harvey P. Dale, <a href="/A210999/b210999.txt">Table of n, a(n) for n = 1..1000</a>

%e Illustration of initial terms of three sequences:

%e A210998:       4,         8, 9, 10,             14, 15, 16

%e A000040: 2, 3,    5,    7,          11,     13,

%e A210999:             6,                 12,

%t Select[Range[4, 200], Not[PrimeQ[#]] && OddQ[PrimePi[#]] &] (* _Alonso del Arte_, Sep 26 2012 *)

%t Flatten[Range[First[#]+1,Last[#]-1]&/@Partition[Prime[Range[3,50]],2]] (* _Harvey P. Dale_, Oct 08 2012 *)

%Y Cf. A002808, A014689, A031215, A031368, A073170, A210998.

%K nonn,easy

%O 1,1

%A _Omar E. Pol_, Sep 26 2012