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 A373554 #9 Jul 04 2024 16:40:47 %S A373554 1,3,5,7,11,16,24,36,53,80,118,177,263,392,585,870,1299,1933,2883, %T A373554 4295,6400,9540,14212,21185,31564,47042,70101,104463,155680,231985, %U A373554 345722,515187,767749,1144111,1704963,2540784,3786288,5642420,8408397 %N A373554 Number of ternary length-2 squarefree words of length n not containing the subwords 021 or 10. %H A373554 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,2,1,-1). %F A373554 a(n) = 2*a(n-2) + a(n-3) - a(n-4). %F A373554 G.f.: ((1+x)*(1+2*x+x^2-x^3))/(1-2*x^2-x^3+x^4). %e A373554 For n=3 the a(3)=7 solutions are 012, 020, 120, 121, 201, 202, 212. %K A373554 nonn,easy %O A373554 0,2 %A A373554 _Miquel A. Fiol_, Jun 09 2024