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 A054439 #3 Mar 30 2012 18:51:20 %S A054439 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,2,3, %T A054439 0,1,0,1,0,0,0,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,4,5,6,7, %U A054439 0,1,2,3,0,1,2,3,0,0,0,1,1,0,0,0,0,0,0,0,0,0,1,0,1,0,3,2,2,3,0,1,0,1,0,0,0 %N A054439 Fourth derivative of n. %F A054439 a(n)=A038554(A038554(A038554(A038554(n))))=A038570(A038570(n)) %Y A054439 Cf. A038554, A038570, A038571. %K A054439 nonn %O A054439 0,33 %A A054439 _Henry Bottomley_, May 11 2000