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 A070207 #38 Sep 08 2022 08:45:05
%S A070207 1,2,3,14,50,181,657,2383,8644,31355,113736,412562,1496513,5428399,
%T A070207 19690785,71425666,259086967,939803018,3409008654,12365718965,
%U A070207 44854977221,162705378247,590191808148,2140841158159,7765612469020,28168711531526,102178200690777
%N A070207 Expansion of (1-x-5*x^2)/(1-3*x-2*x^2-x^3).
%C A070207 The old entry with this sequence number was a duplicate of A024155.
%D A070207 Benoit Rittaud, Elise Janvresse, Emmanuel Lesigne and Jean-Christophe Novelli, Quand les maths se font discrètes, Le Pommier, 2008 (ISBN 978-2-7465-0370-0). See pp. 42ff.
%H A070207 Robert Israel, <a href="/A070207/b070207.txt">Table of n, a(n) for n = 0..1770</a>
%H A070207 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,2,1).
%F A070207 a(0)=1, a(1)=2, a(2)=3, a(n) = 3*a(n-1)+2*a(n-2)+a(n-3). - _Harvey P. Dale_, Feb 01 2013
%p A070207 f:= gfun:-rectoproc({-a(n+3)+3*a(n+2)+2*a(n+1)+a(n), a(0) = 1, a(1) = 2, a(2) = 3},a(n),remember):
%p A070207 map(f, [$0..50]); # _Robert Israel_, Dec 28 2015
%t A070207 CoefficientList[Series[(1-x-5x^2)/(1-3x-2x^2-x^3),{x,0,40}],x] (* or *) LinearRecurrence[{3,2,1},{1,2,3},40] (* _Harvey P. Dale_, Feb 01 2013 *)
%o A070207 (PARI) Vec((1-x-5*x^2)/(1-3*x-2*x^2-x^3) + O(x^100)) \\ _Altug Alkan_, Dec 27 2015
%o A070207 (Magma) I:=[1,2,3]; [n le 3 select I[n] else 3*Self(n-1)+2*Self(n-2)+Self(n-3): n in [1..30]]; // _Vincenzo Librandi_, Dec 28 2015
%K A070207 nonn,easy
%O A070207 0,2
%A A070207 _N. J. A. Sloane_, Sep 18 2008