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 A143750 #2 Mar 30 2012 18:59:21 %S A143750 0,-1,-110,-111000,-1111000000,-111110000000000, %T A143750 -111111000000000000000,-1111111000000000000000000000, %U A143750 -111111110000000000000000000000000000,-111111111000000000000000000000000000000000000 %N A143750 a(n)=10^C(n,2)*(1-10^n)/9. %C A143750 Hankel transform of A143749. %F A143750 a(n)=-10^C(n,2)*A002275(n); %K A143750 easy,sign %O A143750 0,3 %A A143750 _Paul Barry_, Aug 30 2008