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 A014992 #30 Sep 08 2022 08:44:39
%S A014992 1,-9,91,-909,9091,-90909,909091,-9090909,90909091,-909090909,
%T A014992 9090909091,-90909090909,909090909091,-9090909090909,90909090909091,
%U A014992 -909090909090909,9090909090909091,-90909090909090909
%N A014992 a(n) = (1 - (-10)^n)/11.
%C A014992 q-integers for q = -10.
%H A014992 Vincenzo Librandi, <a href="/A014992/b014992.txt">Table of n, a(n) for n = 1..1000</a>
%H A014992 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (-9,10).
%F A014992 a(n) = a(n-1) + q^(n-1) = (q^n - 1) / (q - 1).
%F A014992 G.f.: x/((1 - x)*(1 + 10*x)). - _Vincenzo Librandi_, Oct 22 2012
%F A014992 a(n) = -9*a(n-1) + 10*a(n-2). - _Vincenzo Librandi_, Oct 22 2012
%F A014992 a(n) = (-1)^(n+1)*A015585(n). - _R. J. Mathar_, Oct 26 2015
%F A014992 E.g.f.: (exp(x) - exp(-10*x))/11. - _G. C. Greubel_, May 26 2018
%p A014992 a:=n->sum ((-10)^j, j=0..n): seq(a(n), n=0..25); # _Zerinvary Lajos_, Dec 16 2008
%t A014992 CoefficientList[Series[1/((1 - x)*(1 + 10*x)), {x, 0, 30}], x] (* _Vincenzo Librandi_, Oct 22 2012 *)
%o A014992 (Sage) [gaussian_binomial(n,1,-10) for n in range(1,19)] # _Zerinvary Lajos_, May 28 2009
%o A014992 (Magma) I:=[1, -9]; [n le 2 select I[n] else -9*Self(n-1) +10*Self(n-2): n in [1..30]]; // _Vincenzo Librandi_, Oct 22 2012
%o A014992 (PARI) for(n=1, 30, print1((1-(-10)^n)/11, ", ")) \\ _G. C. Greubel_, May 26 2018
%Y A014992 Cf. A077925, A014983, A014985, A014986, A014987, A014989, A014990, A014991, A014993, A014994. - _Zerinvary Lajos_, Dec 16 2008
%K A014992 sign,easy
%O A014992 1,2
%A A014992 _Olivier Gérard_
%E A014992 Better name from _Ralf Stephan_, Jul 14 2013