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 A245989 #28 Dec 31 2023 11:16:23
%S A245989 1,3,6,8,12,18,26,38,56,82,120,176,258,378,554,812,1190,1744,2556,
%T A245989 3746,5490,8046,11792,17282,25328,37120,54402,79730,116850,171252,
%U A245989 250982,367832,539084,790066,1157898,1696982,2487048,3644946,5341928,7828976,11473922
%N A245989 Number of length n 0..2 arrays with no pair in any consecutive three terms totalling exactly 2.
%C A245989 Also, number of length n ternary words with no pair of equal consecutive letters and avoiding the subwords 010, 101, 020, 202. - _Miquel A. Fiol_, Dec 22 2023
%H A245989 Alois P. Heinz, <a href="/A245989/b245989.txt">Table of n, a(n) for n = 0..2000</a> (210 terms from R. H. Hardin)
%F A245989 a(n) = a(n-1) + a(n-3) for n>=5.
%F A245989 G.f.: (x^4 + x^3 + 3*x^2 + 2*x + 1) / (1 - x - x^3). - _Colin Barker_, Nov 05 2018
%e A245989 Some solutions for n=12:
%e A245989 0 1 0 1 1 0 2 2 0 2 0 2 0 0 0 1
%e A245989 0 2 1 2 0 0 1 2 1 1 0 2 0 0 1 2
%e A245989 0 2 0 2 0 1 2 1 0 2 0 2 0 0 0 2
%e A245989 0 2 0 1 0 0 2 2 0 2 1 1 1 1 0 1
%e A245989 0 1 1 2 0 0 2 2 0 2 0 2 0 0 0 2
%e A245989 0 2 0 2 1 1 2 1 1 1 0 2 0 0 0 2
%e A245989 0 2 0 2 0 0 1 2 0 2 0 2 0 0 1 2
%e A245989 0 2 0 2 0 0 2 2 0 2 0 2 0 0 0 2
%e A245989 0 1 1 2 1 1 2 1 0 2 0 1 1 0 0 1
%e A245989 0 2 0 1 0 0 2 2 0 2 0 2 0 0 0 2
%e A245989 0 2 0 2 0 0 2 2 0 1 1 2 0 0 0 2
%e A245989 0 2 0 2 1 0 1 1 0 2 0 1 0 0 1 2
%t A245989 gf=(x^4 + x^3 + 3*x^2 + 2*x + 1) / (1 - x - x^3);Table[SeriesCoefficient[gf, {x, 0, n}], {n, 0, 40}] (* _James C. McMahon_, Dec 30 2023 *)
%Y A245989 Column 2 of A245995.
%K A245989 nonn,easy
%O A245989 0,2
%A A245989 _R. H. Hardin_, Aug 09 2014
%E A245989 Edited by _Alois P. Heinz_, Dec 30 2023