This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A210998 #12 Sep 27 2012 11:21:43 %S A210998 4,8,9,10,14,15,16,20,21,22,30,38,39,40,44,45,46,54,55,56,57,58,62,63, %T A210998 64,65,66,72,80,81,82,90,91,92,93,94,95,96,102,108,114,115,116,117, %U A210998 118,119,120,121,122,123,124,125,126,132,133,134,135,136 %N A210998 Composite numbers that are in the gap between an even-indexed prime and an odd-indexed prime. %e A210998 Illustration of initial terms of three sequences: %e A210998 A210998: 4, 8, 9, 10, 14, 15, 16 %e A210998 A000040: 2, 3, 5, 7, 11, 13, %e A210998 A210999: 6, 12, %t A210998 Select[Range[4, 200], Not[PrimeQ[#]] && EvenQ[PrimePi[#]] &] (* _Alonso del Arte_, Sep 26 2012 *) %Y A210998 Cf. A002808, A014689, A031215, A031368, A073170, A210999. %K A210998 nonn,easy %O A210998 1,1 %A A210998 _Omar E. Pol_, Sep 26 2012