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 A077864 #27 Sep 29 2015 07:18:30
%S A077864 1,2,5,11,24,52,112,241,518,1113,2391,5136,11032,23696,50897,109322,
%T A077864 234813,504355,1083304,2326828,4997792,10734753,23057166,49524465,
%U A077864 106373551,228479648,490751216,1054084064,2264066145,4862985490,10445201845,22435238971,48188628152
%N A077864 Expansion of (1-x)^(-1)/(1-x-2*x^2-x^3).
%C A077864 Diagonal sums of triangle using cumulative sums of odd-indexed rows of Pascal's triangle (cf. A020988). - _Paul Barry_, May 18 2003
%H A077864 Alois P. Heinz, <a href="/A077864/b077864.txt">Table of n, a(n) for n = 0..1000</a>
%H A077864 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2, 1, -1, -1).
%F A077864 a(0)=1, a(1)=2, a(2)=5, a(3)=11, a(n)=2*a(n-1)+a(n-2)-a(n-3)-a(n-4) for n>3. - _Philippe Deléham_, Oct 25 2006
%F A077864 a(n) = term (4,1) in the 4x4 matrix [1,1,0,0; 2,0,1,0; 1,0,0,0; 1,0,0,1]^(n+1). - _Alois P. Heinz_, Jul 24 2008
%F A077864 Conjecture: a(n) = Sum_{j=0..n/2} A027907(n+1-j,2*j+1), n >= 0. - _Werner Schulte_, Sep 29 2015
%p A077864 a := n -> (Matrix([[1,1,0,0], [2,0,1,0], [1,0,0,0], [1,0,0,1]])^(n+1))[4,1]; seq(a(n), n=0..50); # _Alois P. Heinz_, Jul 24 2008
%t A077864 CoefficientList[Series[(1-x)^(-1)/(1-x-2x^2-x^3),{x,0,40}],x] (* or *) LinearRecurrence[{2,1,-1,-1},{1,2,5,11},40] (* _Harvey P. Dale_, Oct 08 2014 *)
%o A077864 (PARI) Vec((1-x)^(-1)/(1-x-2*x^2-x^3)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 26 2012
%K A077864 nonn,easy
%O A077864 0,2
%A A077864 _N. J. A. Sloane_, Nov 17 2002