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 A050684 #10 Oct 15 2019 01:34:21
%S A050684 1,2,20,38,290,542,3710,6878,44390,81902,509510,937118,5685590,
%T A050684 10434062,62170310,113906558,669532790,1225159022,7125795110,
%U A050684 13026431198,75132155990,137237880782,786189403910,1435140927038
%N A050684 Number of nonzero palindromes < 10^n and containing at least one digit '1'.
%H A050684 G. C. Greubel, <a href="/A050684/b050684.txt">Table of n, a(n) for n = 1..1000</a>
%H A050684 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,19,0,-90).
%F A050684 a(2n) = 2*(10^n - 9^n); a(2n + 1) = 2*(10^n - 9^n) + 9*10^n - 8*9^n. - _David Wasserman_, Feb 14 2002
%e A050684 Up to 10^2 we find two numbers 1 and 11.
%t A050684 Table[If[EvenQ[n], 2*(10^(n/2) - 9^(n/2)) , 2*(10^((n - 1)/2) - 9^((n - 1)/2)) + 9*10^((n - 1)/2) - 8*9^((n - 1)/2)], {n, 25}] (* or *) LinearRecurrence[{0, 19, 0, -90},{1, 2, 20, 38},25] (* _G. C. Greubel_, Oct 27 2016 *)
%Y A050684 Cf. A050250, A050685.
%K A050684 nonn,base
%O A050684 1,2
%A A050684 _Patrick De Geest_, Aug 15 1999
%E A050684 More terms from _David Wasserman_, Feb 14 2002