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 A108152 #6 Jun 06 2016 17:29:22
%S A108152 1,0,2,7,25,91,330,1197,4342,15750,57131,207235,751717,2726752,
%T A108152 9890925,35877996,130142590,472074687,1712387237,6211453675,
%U A108152 22531210186,81728925145,296460649482,1075371008922,3900763250875,14149492419951
%N A108152 a(n)= 3*a(n-1) +2*a(n-2) +a(n-3).
%H A108152 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,2,1).
%F A108152 G.f.: (-1+3*x)/(-1+3*x+2*x^2+x^3). [Sep 28 2009]
%F A108152 a(n) = A108153(n+1) -3*A108153(n). [Sep 28 2009]
%t A108152 M = {{0, 1, 0}, {0, 0, 1}, {1, 2, 3}} a3 = Table[MatrixPower[M, i][[1, 2]], {i, 1, 50}]
%t A108152 LinearRecurrence[{3,2,1},{1,0,2},30] (* _Harvey P. Dale_, Jun 06 2016 *)
%Y A108152 Cf. A000073, A001590.
%K A108152 nonn,easy
%O A108152 0,3
%A A108152 _Roger L. Bagula_, Jun 06 2005
%E A108152 Definition replaced by recurrence by the Associate Editors of the OEIS, Sep 28 2009