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 A198686 #22 Sep 08 2022 08:45:59
%S A198686 3,27,195,1371,9603,67227,470595,3294171,23059203,161414427,
%T A198686 1129900995,7909306971,55365148803,387556041627,2712892291395,
%U A198686 18990246039771,132931722278403,930522055948827,6513654391641795,45595580741492571
%N A198686 4*7^n-1.
%H A198686 Vincenzo Librandi, <a href="/A198686/b198686.txt">Table of n, a(n) for n = 0..1000</a>
%H A198686 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (8,-7).
%F A198686 a(n) = 7*a(n-1)+6. a(n) = 8*a(n-1)-7*a(n-2), n>1.
%F A198686 G.f. ( 3+3*x ) / ( (7*x-1)*(x-1) ). - R. J. Mathar, Oct 30 2011
%t A198686 4*7^Range[0,20]-1 (* or *) LinearRecurrence[{8,-7},{3,27},20] (* _Harvey P. Dale_, Dec 27 2011 *)
%o A198686 (Magma) [4*7^n-1: n in [0..30]]
%Y A198686 Cf. A048473, A081655, A198480, A198647.
%K A198686 nonn,easy
%O A198686 0,1
%A A198686 _Vincenzo Librandi_, Oct 29 2011