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 A165511 #21 Sep 08 2022 08:45:47
%S A165511 1,10,80,820,6380,67420,506780,5561020,40049180,460442620,3143983580,
%T A165511 38295852220,244662669980,3201964029820,18817676268380,
%U A165511 269359086415420,1424231777738780,22818085999649020,105362773996841180
%N A165511 a(0)=1, a(1)=10, a(n) = 90*a(n-2) - a(n-1).
%C A165511 a(n)/a(n-1) tends to -10.
%C A165511 First entry < 0: a(30) = -8009307078719785774426912420.
%H A165511 G. C. Greubel, <a href="/A165511/b165511.txt">Table of n, a(n) for n = 0..998</a> (terms 0..100 from Franklin T. Adams-Watters)
%H A165511 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-1, 90).
%F A165511 G.f.: (1+11*x)/(1+x-90*x^2).
%F A165511 a(n) = Sum_{k=0..n} A112555(n,k)*9^k.
%F A165511 a(n) = (20*9^n-(-10)^n)/19. - _Klaus Brockhaus_, Sep 26 2009
%F A165511 E.g.f.: (20*exp(9*x) - exp(-10*x))/19. - _G. C. Greubel_, Oct 21 2018
%t A165511 LinearRecurrence[{-1,90},{1,10},20] (* or *) CoefficientList[Series[ (1+11x)/(1+x-90x^2),{x,0,20}],x] (* _Harvey P. Dale_, Apr 30 2011 *)
%o A165511 (PARI) vector(50, n, n--; (20*9^n-(-10)^n)/19) \\ _G. C. Greubel_, Oct 21 2018
%o A165511 (Magma) [(20*9^n-(-10)^n)/19: n in [0..50]]; // _G. C. Greubel_, Oct 21 2018
%K A165511 sign
%O A165511 0,2
%A A165511 _Philippe Deléham_, Sep 21 2009