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 A117865 #12 Oct 27 2016 03:16:49
%S A117865 5,10,40,70,250,430,1510,2590,9070,15550,54430,93310,326590,559870,
%T A117865 1959550,3359230,11757310,20155390,70543870,120932350,423263230,
%U A117865 725594110,2539579390,4353564670,15237476350,26121388030,91424858110,156728328190,548549148670
%N A117865 Number of palindromes (in base 6) below 6^n.
%H A117865 G. C. Greubel, <a href="/A117865/b117865.txt">Table of n, a(n) for n = 1..1000</a>
%H A117865 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,6,-6).
%F A117865 a(n) = 7*6^((n-1)/2)-2 (n odd), 2*6^(n/2)-2 (n even).
%F A117865 G.f.: 5*x*(x+1) / ((x-1)*(6*x^2-1)). - _Colin Barker_, Feb 15 2013
%t A117865 Table[If[OddQ[n], 7*6^((n - 1)/2) - 2, 2*6^(n/2) - 2], {n,25}] (* or *) LinearRecurrence[{1,6,-6},{5, 10, 40},25] (* _G. C. Greubel_, Oct 27 2016 *)
%Y A117865 Cf. A050250.
%K A117865 nonn,base,easy
%O A117865 1,1
%A A117865 _Martin Renner_, May 02 2006
%E A117865 More terms from _Colin Barker_, Feb 15 2013