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 A171226 #17 Dec 15 2017 17:37:09
%S A171226 19,919,90109,9001009,900010009,90000100009,9000001000009,
%T A171226 900000010000009,90000000100000009,9000000001000000009,
%U A171226 900000000010000000009,90000000000100000000009,9000000000001000000000009,900000000000010000000000009,90000000000000100000000000009
%N A171226 9+10^n+9*100^n.
%H A171226 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (111, -1110, 1000).
%F A171226 a(n) = 111*a(n-1) -1110*a(n-2) +1000*a(n-3).
%F A171226 G.f.: -(19-1190*x+9190*x^2)/((x-1) * (100*x-1) * (10*x-1)). - _R. J. Mathar_, Feb 14 2010
%p A171226 A171226:=n->9+10^n+9*100^n; seq(A171226(n), n=0..20); # _Wesley Ivan Hurt_, Mar 07 2014
%t A171226 LinearRecurrence[{111,-1110,1000},{19,919,90109},20] (* _Harvey P. Dale_, Oct 24 2011 *)
%o A171226 (PARI) a(n) = 9+10^n+9*100^n; \\ _Michel Marcus_, Mar 08 2014
%Y A171226 Cf. A083816.
%K A171226 easy,nonn
%O A171226 0,1
%A A171226 _Jason Earls_, Dec 05 2009