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 A198693 #18 Sep 08 2022 08:45:59
%S A198693 2,11,47,191,767,3071,12287,49151,196607,786431,3145727,12582911,
%T A198693 50331647,201326591,805306367,3221225471,12884901887,51539607551,
%U A198693 206158430207,824633720831,3298534883327,13194139533311,52776558133247
%N A198693 a(n) = 3*4^n-1.
%H A198693 Vincenzo Librandi, <a href="/A198693/b198693.txt">Table of n, a(n) for n = 0..1000</a>
%H A198693 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (5,-4).
%F A198693 a(n) = 4*a(n-1)+3.
%F A198693 a(n) = 5*a(n-1) - 4*a(n-2), for n > 1.
%F A198693 G.f.: (2+x)/((4*x-1)*(x-1)). - _R. J. Mathar_, Oct 30 2011
%t A198693 3*4^Range[0,30]-1 (* or *) LinearRecurrence[{5,-4},{2,11},30] (* _Harvey P. Dale_, Jul 04 2017 *)
%o A198693 (Magma) [3*4^n-1: n in [0..30]]
%Y A198693 Cf. A024036, A097743, A114569, A156760.
%K A198693 nonn,easy
%O A198693 0,1
%A A198693 _Vincenzo Librandi_, Oct 29 2011