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 A174653 #10 Aug 19 2019 14:18:35
%S A174653 4,6,46,49,51,55,62,65,69,74,77,82,91,106,111,115,129,155,161,166,169,
%T A174653 183,185,187,194,209,221,226,235,237,247,249,259,262,265,267,274,278,
%U A174653 287,289,291,295,305,309,314,319,321,323,329,339,341,346,355,358,365
%N A174653 Semiprimes s such that neither s-1 nor s+1 is semiprime.
%C A174653 A064911(a(n))*(1 - A064911(a(n)-1))*(1 - A064911(a(n)+1)) = 1. - _Reinhard Zumkeller_, Apr 03 2010
%H A174653 R. Zumkeller, <a href="/A174653/b174653.txt">Table of n, a(n) for n = 1..1000</a>
%e A174653 a(1)=4 because 4-1 = 3 (not semiprime) and 4+1 = 5 (not semiprime).
%t A174653 Mean/@SequencePosition[Table[If[PrimeOmega[n]==2,1,0],{n,400}],{0,1,0}] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Aug 19 2019 *)
%Y A174653 Cf. A001358, A100959.
%K A174653 nonn
%O A174653 1,1
%A A174653 _Juri-Stepan Gerasimov_, Mar 25 2010
%E A174653 Corrected by _Reinhard Zumkeller_ and _Ray Chandler_, Apr 07 2010