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 A078044 #12 Jun 13 2015 00:50:49 %S A078044 1,-2,2,-4,8,-12,20,-36,60,-100,172,-292,492,-836,1420,-2404,4076, %T A078044 -6916,11724,-19876,33708,-57156,96908,-164324,278636,-472452,801100, %U A078044 -1358372,2303276,-3905476,6622220,-11228772,19039724,-32284164,54741708,-92821156,157389484,-266872900 %N A078044 Expansion of (1-x)/(1+x+2*x^3). %H A078044 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-1,0,-2). %o A078044 (PARI) Vec((1-x)/(1+x+2*x^3)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 27 2012 %Y A078044 Equals 4 * (-1)^n * A003476(n-2), n>2. %Y A078044 First differences of A077974. %K A078044 sign,easy %O A078044 0,2 %A A078044 _N. J. A. Sloane_, Nov 17 2002