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 A113523 #9 Apr 09 2014 10:12:21
%S A113523 0,0,0,4,4,6,6,8,9,10,10,12,12,14,15,16,16,18,18,20,21,22,22,24,25,26,
%T A113523 27,28,28,30,30,32,33,34,35,36,36,38,39,40,40,42,42,44,45,46,46,48,49,
%U A113523 50,51,52,52,54,55,56,57,58,58,60,60,62,63,64,65,66,66,68,69,70,70,72
%N A113523 a(n) = largest composite nonnegative integer <= n.
%C A113523 For n > 3: a(n) = A179278(n). [From _Reinhard Zumkeller_, Jul 08 2010]
%F A113523 a(1)=a(2)=a(3) = 0. For n >= 4, a(n) = A014684(n).
%t A113523 nnci[n_]:=Module[{k=0},While[PrimeQ[n-k],k++];n-k]/.{1->0}; Array[nnci,80] (* _Harvey P. Dale_, Jul 19 2012 *)
%Y A113523 Cf. A007917, A014684.
%K A113523 nonn
%O A113523 1,4
%A A113523 _Leroy Quet_, Jan 12 2006