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 A373447 #17 Aug 04 2025 13:11:52
%S A373447 1,3,6,9,14,23,36,57,90,143,226,357,566,895,1416,2241,3546,5611,8878,
%T A373447 14049,22230,35175,55660,88073,139362,220519,348938,552141,873678,
%U A373447 1382463,2187536,3461441,5477202,8666835,13713942,21700217,34337278,54333495,85974452
%N A373447 Number of ternary strings of length n avoiding the substrings 00, 11, 22, 121, 212, 202.
%H A373447 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,2,1,0,-1).
%F A373447 a(n) = a(n-2) + 2*a(n-3) + a(n-4) - a(n-6).
%F A373447 G.f.: (x+1)*(x^2+x+1)*(x^3-x^2-x-1)/(-x^6+x^4+2*x^3+x^2-1). - _Alois P. Heinz_, Jun 05 2024
%e A373447 For n=3 the a(3)=9 solutions are 010, 012, 020, 021, 101, 102, 120, 201, 210.
%t A373447 LinearRecurrence[{0,1,2,1,0,-1},{1,3,6,9,14,23,36},40] (* _Harvey P. Dale_, Aug 04 2025 *)
%Y A373447 Cf. A003945.
%K A373447 nonn,easy
%O A373447 0,2
%A A373447 _Miquel A. Fiol_, Jun 05 2024