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 A178869 #36 Dec 18 2023 12:20:48
%S A178869 0,1,9,71,549,4231,32589,250991,1933029,14887351,114655869,883029311,
%T A178869 6800705109,52376052871,403377424749,3106636294031,23925952398789,
%U A178869 184267208648791,1419145353851229,10929636098173151,84175271345046069
%N A178869 a(n) = 9*a(n-1) - 10*a(n-2); a(0)=0, a(1)=1.
%C A178869 Alternating row sums of triangle A206819. Large Schroeder numbers in decimal expansion of ratio a(n)/a(n+1). [A-number corrected by _Philippe Deléham_, Feb 26 2013]
%H A178869 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (9, -10).
%F A178869 G.f.: -x/(-10*x^2+9*x-1).
%F A178869 a(n) = 9a(n-1)-10a(n-2), a(0)=0, a(1)=1. [_Harvey P. Dale_, May 06 2011]
%F A178869 a(n+1) = Sum_{k, 0<=k<=n}A206819(n,k)*(-1)^k. - _Philippe Deléham_, Feb 26 2013
%t A178869 Join[{a=0,b=1},Table[c=9*b-10*a+2;a=b;b=c,{n,60}]] (* _Vladimir Joseph Stephan Orlovsky_, Jan 20 2011 *)
%t A178869 LinearRecurrence[{9,-10},{0,1},50] (* or *) CoefficientList[Series[ -x/(-10x^2+9x-1),{x,0,50}],x] (* _Harvey P. Dale_, May 06 2011 *)
%Y A178869 Cf. A006318, A171415, A104562, A206819.
%K A178869 nonn,easy
%O A178869 0,3
%A A178869 _Mark Dols_, Jun 20 2010