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 A117868 #14 Jun 13 2015 00:52:05
%S A117868 8,16,88,160,808,1456,7288,13120,65608,118096,590488,1062880,5314408,
%T A117868 9565936,47829688,86093440,430467208,774840976,3874204888,6973568800,
%U A117868 34867844008,62762119216,313810596088,564859072960,2824295364808,5083731656656,25418658283288
%N A117868 Number of palindromes (in base 9) below 9^n.
%H A117868 Colin Barker, <a href="/A117868/b117868.txt">Table of n, a(n) for n = 1..1000</a>
%H A117868 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,9,-9).
%F A117868 a(n) = 10*9^((n-1)/2)-2 (n odd), 2*9^(n/2)-2 (n even).
%F A117868 a(1)=0, a(2)=8, a(3)=16, a(n)=a(n-1)+9*a(n-2)-9*a(n-3). - _Harvey P. Dale_, Jul 17 2012
%F A117868 G.f.: 8*x*(x+1) / ((x-1)*(3*x-1)*(3*x+1)). - _Colin Barker_, Apr 26 2015
%F A117868 a(n) = 8 * 3^(n-1) + 2 * (-3)^(n-1) - 2. - _Robert Israel_, Apr 26 2015
%p A117868 seq( 8 * 3^(n-1) + 2 * (-3)^(n-1) - 2, n=1..100); # _Robert Israel_, Apr 26 2015
%t A117868 Table[If[OddQ[n],10*9^((n-1)/2)-2,2*9^(n/2)-2],{n,0,30}] (* or *) LinearRecurrence[ {1,9,-9},{0,8,16},30] (* _Harvey P. Dale_, Jul 17 2012 *)
%o A117868 (PARI) Vec(8*x*(x+1)/((x-1)*(3*x-1)*(3*x+1)) + O(x^100)) \\ _Colin Barker_, Apr 26 2015
%Y A117868 Cf. A050250.
%K A117868 nonn,base,easy
%O A117868 1,1
%A A117868 _Martin Renner_, May 02 2006
%E A117868 More terms from _Harvey P. Dale_, Jul 17 2012