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 A089827 #3 Mar 30 2012 18:50:42
%S A089827 2,4,8,16,24,48,80,160,320,640,1280,2560,3840,7680,15360,30720,61440,
%T A089827 122880,184320,368640,737280,1474560,2949120,5898240,11796480,
%U A089827 23592960,47185920,94371840,188743680,377487360,566231040
%N A089827 Number of subsets of {1,.., n} containing no twin prime pairs.
%C A089827 a(n) = A000079(n) - A089828(n).
%F A089827 a(n) = if n and n-2 are primes then (if n=7 then a(n-1)*5/3 else a(n-1)*3/2) else a(n-2)*2.
%Y A089827 Cf. A071538, A001359, A006512.
%K A089827 nonn
%O A089827 1,1
%A A089827 _Reinhard Zumkeller_, Nov 12 2003