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 A155041 #5 Jun 13 2015 00:52:47 %S A155041 1,1,2,0,1,-1,2,0,3,-1,2,-2,3,-1,4,-2,3,-3,4,-2,5,-3,4,-4,5,-3,6,-4,5, %T A155041 -5,6,-4,7,-5,6,-6,7,-5,8,-6,7,-7,8,-6,9,-7,8,-8,9,-7,10,-8,9,-9,10, %U A155041 -8,11,-9,10,-10,11,-9,12,-10,11,-11,12,-10,13,-11,12,-12,13,-11,14,-12,13 %N A155041 Diagonal sums of symmetric (1,-1)-triangle A155040. %C A155041 First differences of A155041 are (-1)^n*A008611. %H A155041 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,-1,0,1). %F A155041 G.f.: (1+x+x^2)/(1-x^2+x^3-x^5); %F A155041 a(2n)=A008611(n+2)=[x^n](1+x-x^2)/(1-x-x^3+x^4); a(2n+1)=[x^n](1-x-x^2)/(1-x-x^3+x^4). %K A155041 easy,sign %O A155041 0,3 %A A155041 _Paul Barry_, Jan 19 2009