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 A083812 #9 Jun 13 2015 00:51:03
%S A083812 18,198,1998,19998,199998,1999998,19999998,199999998,1999999998,
%T A083812 19999999998,199999999998,1999999999998,19999999999998,
%U A083812 199999999999998,1999999999999998,19999999999999998,199999999999999998,1999999999999999998,19999999999999999998
%N A083812 4n-1 is the digit reversal of n-1.
%C A083812 1. a(n) = 18 + 180 + 1800+ ...+ up to n terms. a(n) = sum of n terms of the geometric progression with the first term 18 and common ratio 10. 2. a(n) = 18*A000042(n).( the unary sequence).
%H A083812 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11, -10).
%F A083812 a(n) = 2*(10^n - 1).
%F A083812 a(1)=18, a(2)=198, a(n)=11*a(n-1)-10*a(n-2). - _Harvey P. Dale_, Apr 24 2015
%e A083812 18 -1 = 17, 4*18 - 1 = 71.
%t A083812 Accumulate[NestList[10#&,18,20]] (* or *) LinearRecurrence[{11,-10},{18,198},20] (* _Harvey P. Dale_, Apr 24 2015 *)
%Y A083812 Cf. A000042, A083811.
%K A083812 base,nonn
%O A083812 1,1
%A A083812 _Amarnath Murthy_ and Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 08 2003
%E A083812 Corrected and extended by _Harvey P. Dale_, Apr 24 2015