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 A097041 #17 May 01 2017 02:58:05
%S A097041 1,1,1,10,10,19,100,109,271,1009,1252,3448,10333,14716,41365,107713,
%T A097041 173809,479998,1143226,2044279,5463208,12333313,23861719,61502185,
%U A097041 134861536,276257656,688381201,1490011480,3174700105,7685442289
%N A097041 Expansion of (1+x)/(1-x^2-9*x^3).
%H A097041 G. C. Greubel, <a href="/A097041/b097041.txt">Table of n, a(n) for n = 0..1000</a>
%H A097041 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,9).
%F A097041 a(n) = a(n-2) + 9*a(n-3).
%F A097041 a(n) = Sum_{k=0..floor(n/2)} binomial(floor((n-k)/2), k)*9^k.
%t A097041 CoefficientList[Series[(1+x)/(1-x^2-9x^3),{x,0,30}],x] (* or *) LinearRecurrence[{0,1,9},{1,1,1},30] (* _Harvey P. Dale_, Mar 12 2015 *)
%o A097041 (PARI) x='x+O('x^50); Vec((1+x)/(1-x^2-9*x^3)) \\ _G. C. Greubel_, Apr 30 2017
%Y A097041 Cf. A015445.
%K A097041 easy,nonn
%O A097041 0,4
%A A097041 _Paul Barry_, Jul 20 2004