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 A108012 #17 Aug 11 2017 16:00:01
%S A108012 0,4,18,76,320,1360,5832,25200,109568,478784,2100512,9244352,40784896,
%T A108012 180284672,798121088,3537391360,15692333056,69661541376,309407486464,
%U A108012 1374824795136,6110847909888,27168232722432,120809925167104
%N A108012 a(n)= 8*a(n-1) -16*a(n-2) +4*a(n-4).
%H A108012 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (8,-16,0,4)
%F A108012 G.f.: 2*x*(-2+7*x+2*x^2)/( (2*x^2+4*x-1) * (2*x^2-4*x+1)). [Sep 28 2009]
%F A108012 a(n) = A111567(n-1) + A090017(n+1) - A090017(n) - A090017(n-1), n>0.
%t A108012 M = {{0, 0, 0, 2}, {1, 4, 0, 0}, {0, 2, 0, 0}, {0, 0, 1, 4}} v[1] = {0, 1, 1, 2}; v[n_] := v[n] = M.v[n - 1]; digits = 50; a = Table[v[n][[1]], {n, 1, digits}]
%t A108012 LinearRecurrence[{8,-16,0,4},{0,4,18,76},30] (* _Harvey P. Dale_, Aug 11 2017 *)
%K A108012 nonn,easy
%O A108012 0,2
%A A108012 _Roger L. Bagula_, May 30 2005
%E A108012 Definition replaced by recurrence by the Associate Editors of the OEIS, Sep 28 2009