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 A214260 #34 Apr 18 2022 10:46:26
%S A214260 0,1,3,6,13,29,64,141,311,686,1513,3337,7360,16233,35803,78966,174165,
%T A214260 384133,847232,1868629,4121391,9090014,20048657,44218705,97527424,
%U A214260 215103505,474425715,1046378854,2307861213
%N A214260 First differences of A052980.
%C A214260 1 -> 123, 2 -> 12, 3 -> 2, starting with 1 gives the sequence: 1, 123, 123122, 1231221231212, ... the n-th term has a(n) digits.
%C A214260 Ternary words of length n-1 with subwords (0,1), (1,1) and (1,2) not allowed. - _Olivier Gérard_, Aug 28 2012
%H A214260 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,1).
%F A214260 Recurrence: a(0) = 0, a(1) = 1, a(2) = 3, a(n+1) = 2*a(n) + a(n-2).
%F A214260 G.f.: x*(1+x)/(1-2*x-x^3).
%F A214260 a(n) = A052980(n) + A052980(n-2) = A052980(n+1) - A052980(n).
%F A214260 a(n+1) = A078061(n)*(-1)^n.
%F A214260 a(0) = 0, a(n) = A008998(n-1) + A008998(n-2) for n>0.
%F A214260 a(n+1) = Sum_{k=0..n} C(n-k, floor(k/2))*2^(n-k-floor(k/2)).
%t A214260 LinearRecurrence[{2,0,1},{0,1,3},30] (* _Harvey P. Dale_, Sep 04 2017 *)
%Y A214260 Cf. A008998, A052980, A064353, A078061.
%K A214260 nonn
%O A214260 0,3
%A A214260 _Philippe Deléham_, Jul 22 2012