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 A109266 #5 Jun 13 2015 00:51:52 %S A109266 1,-1,0,-2,1,-2,3,-3,5,-6,8,-11,14,-19,25,-33,44,-58,77,-102,135,-179, %T A109266 237,-314,416,-551,730,-967,1281,-1697,2248,-2978,3945,-5226,6923, %U A109266 -9171,12149,-16094,21320,-28243,37414,-49563,65657,-86977,115220,-152634,202197,-267854,354831,-470051,622685,-824882 %N A109266 Diagonal sums of Riordan array (1-x-x^2,x(1-x)). %H A109266 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,-1). %F A109266 G.f.: (1-x-x^2)/(1-x^2+x^3); a(n)=a(n-2)-a(n-3). %K A109266 easy,sign %O A109266 0,4 %A A109266 _Paul Barry_, Jun 24 2005