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 A317975 #15 Sep 13 2018 02:41:31
%S A317975 0,1,1,0,4,9,25,76,216,625,1809,5224,15100,43641,126121,364500,
%T A317975 1053424,3044449,8798625,25428496,73489716,212389225,613816249,
%U A317975 1773961884,5126845000,14816857041,42821511601,123756465400,357662823084,1033664743129,2987346551625
%N A317975 a(n) = 2*(a(n-1)+a(n-2)+a(n-3))-a(n-4) for n >= 4, with initial terms 0, 1, 1, 0.
%H A317975 Andrew Howroyd, <a href="/A317975/b317975.txt">Table of n, a(n) for n = 0..1000</a>
%H A317975 H. S. M. Coxeter, <a href="http://gdz.sub.uni-goettingen.de/dms/resolveppn/?PPN=GDZPPN002022109">Loxodromic sequences of tangent spheres</a>, Aequationes Mathematicae, 1.1-2 (1968): 104-121. See p. 112.
%H A317975 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,2,2,-1)
%F A317975 G.f.: x*(1 - x - 4*x^2)/(1 - 2*x - 2*x^2 - 2*x^3 + x^4). - _Andrew Howroyd_, Sep 08 2018
%t A317975 LinearRecurrence[{2, 2, 2, -1}, {0, 1, 1, 0}, 31] (* _Jean-François Alcover_, Sep 13 2018 *)
%o A317975 (PARI) concat([0], Vec((1 - x - 4*x^2)/(1 - 2*x - 2*x^2 - 2*x^3 + x^4) + O(x^40))) \\ _Andrew Howroyd_, Sep 08 2018
%K A317975 nonn,easy
%O A317975 0,5
%A A317975 _N. J. A. Sloane_, Sep 03 2018
%E A317975 Terms a(10) and beyond from _Andrew Howroyd_, Sep 08 2018