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 A078047 #12 Apr 07 2020 03:36:59 %S A078047 1,-2,1,-1,4,-5,3,-6,13,-13,12,-25,39,-38,49,-89,116,-125,187,-294, %T A078047 357,-437,668,-945,1151,-1542,2281,-3041,3844,-5365,7603,-9926,13053, %U A078047 -18333,25132,-32905,44439,-61798,83169,-110249,150676,-206765,276587,-371174,508117,-690117,924348,-1250465 %N A078047 Expansion of (1-x)/(1+x+x^2+2*x^3). %H A078047 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-1,-1,-2). %o A078047 (PARI) Vec((1-x)/(1+x+x^2+2*x^3) + O(x^50)) \\ _Jinyuan Wang_, Apr 07 2020 %Y A078047 First differences of A077976. %K A078047 sign,easy %O A078047 0,2 %A A078047 _N. J. A. Sloane_, Nov 17 2002