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 A080920 #23 Jan 09 2018 01:45:57
%S A080920 0,1,2,39,148,1661,8502,75139,447848,3525561,22725802,168846239,
%T A080920 1133095548,8175809461,56009963102,398173257339,2756695223248,
%U A080920 19449454453361,135383241720402,951497389308439,6641408238830948
%N A080920 a(n) = 2a(n-1) + 35a(n-2), a(0)=0, a(1)=1.
%H A080920 Vincenzo Librandi, <a href="/A080920/b080920.txt">Table of n, a(n) for n = 0..200</a>
%H A080920 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,35).
%F A080920 a(n) = 7^n/12 - (-5)^n/12.
%F A080920 a(n) = Sum{k=1..n, binomial(n, 2k-1)*6^(2(k-1))}.
%F A080920 G.f.: 1/((1+5x)(1-7x)).
%F A080920 a(n+1) = Sum_{k = 0..n} A238801(n,k)*6^k. - _Philippe Deléham_, Mar 07 2014
%t A080920 Join[{a=0,b=1},Table[c=2*b+35*a;a=b;b=c,{n,60}]] (* _Vladimir Joseph Stephan Orlovsky_, Feb 01 2011 *)
%t A080920 CoefficientList[Series[1 / ((1 + 5 x) (1 - 7 x)), {x, 0, 20}], x] (* _Vincenzo Librandi_, Aug 05 2013 *)
%t A080920 LinearRecurrence[{2,35},{0,1},30] (* _Harvey P. Dale_, Aug 24 2017 *)
%Y A080920 Cf. A079773, A051958, A015441.
%K A080920 easy,nonn
%O A080920 0,3
%A A080920 _Paul Barry_, Feb 24 2003