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 A288219 #15 Apr 07 2020 20:50:07
%S A288219 2,4,7,11,18,29,47,76,123,199,322,521,843,1364,2207,3571,5778,9349,
%T A288219 15127,24476,39603,64079,103682,167761,271443,439204,710647,1149851,
%U A288219 1860498,3010349,4870847,7881196,12752043,20633239,33385282,54018521,87403803,141422324
%N A288219 a(n) = a(n-1) + a(n-2) for n >= 3, where a(0) = 2, a(1) = 4, a(2) = 7.
%C A288219 Empirically, a(n) is the number of letters (0's and 1's) in the n-th iterate of the mapping 00->1000, 10->010, starting with 00; see A288216.
%H A288219 Clark Kimberling, <a href="/A288219/b288219.txt">Table of n, a(n) for n = 0..2000</a>
%H A288219 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (1, 1).
%F A288219 a(n) = a(n-1) + a(n-2) for n >= 3, where a(0) = 2, a(1) = 4, a(2) = 7.
%F A288219 a(n) = L(n+2) for n >=1, where L = A000032 (Lucas numbers).
%F A288219 G.f.: (-2 - 2 x - x^2)/(-1 + x + x^2).
%t A288219 Join[{2}, LinearRecurrence[{1, 1}, {4, 7}, 40]]
%Y A288219 Cf. A288216, A163695, A080023, A000204.
%K A288219 nonn,easy
%O A288219 0,1
%A A288219 _Clark Kimberling_, Jun 19 2017