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 A016211 #25 Feb 06 2018 15:13:17
%S A016211 1,10,73,478,2989,18298,110881,668566,4021237,24156946,145030249,
%T A016211 870447214,5223480445,31343274154,188066819377,1128422439622,
%U A016211 6770599207813,40623788957122,243743314873465
%N A016211 Expansion of 1/((1-x)(1-3x)(1-6x)).
%H A016211 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (10,-27,18).
%F A016211 a(n) = 9*a(n-1) - 18*a(n-2) + 1. - _Vincenzo Librandi_, Feb 10 2011
%F A016211 a(n) = 2*6^(n+1)/5 - 3^(n+1)/2 + 1/10. - _R. J. Mathar_, Feb 10 2011
%F A016211 a(n) = Sum_{k=0...n} 2^(k-1)*(3^(n+1) - 3^k). - _J. M. Bergot_, Feb 06 2018
%p A016211 a:=n->sum((6^(n-j+1)-3^(n-j+1))/3, j=0..n+1): seq(a(n), n=0..19); # _Zerinvary Lajos_, Jan 15 2007
%o A016211 (PARI) Vec(1/((1-x)*(1-3*x)*(1-6*x))+O(x^99)) \\ _Charles R Greathouse IV_, Sep 26 2012
%K A016211 nonn,easy
%O A016211 0,2
%A A016211 _N. J. A. Sloane_