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 A213469 #6 Jun 02 2025 08:02:20 %S A213469 157,7803,191573,3737885,67329406,1167362677,19808276303,331605526490, %T A213469 5501075085468,90671574326172,1487390263956378,24310876230706073, %U A213469 396224883822318038,6443121835406288422,104579933906413425698 %N A213469 Number of 0..3 arrays of length 2*n+4 with sum less than 3*n in any length 2n subsequence (=less than 50% duty cycle). %C A213469 Row 5 of A213464 %H A213469 R. H. Hardin, <a href="/A213469/b213469.txt">Table of n, a(n) for n = 1..210</a> %e A213469 Some solutions for n=3 %e A213469 ..0....0....2....2....2....0....0....0....0....0....2....0....0....0....0....0 %e A213469 ..2....1....1....0....0....0....0....0....1....0....2....1....3....2....3....0 %e A213469 ..3....1....3....2....1....2....0....1....0....3....1....2....1....0....1....1 %e A213469 ..1....3....0....0....0....0....3....0....0....2....0....2....0....2....0....1 %e A213469 ..0....0....0....0....0....1....2....1....1....0....1....0....1....1....0....0 %e A213469 ..1....0....0....1....3....1....0....0....0....2....0....0....2....0....1....1 %e A213469 ..1....0....2....1....1....0....0....2....1....1....0....1....0....2....1....1 %e A213469 ..1....2....1....3....0....1....0....2....1....0....0....2....0....1....0....0 %e A213469 ..2....0....1....2....0....2....0....0....3....0....0....0....2....0....0....1 %e A213469 ..1....3....1....0....0....3....1....2....0....3....0....2....2....0....0....0 %K A213469 nonn %O A213469 1,1 %A A213469 _R. H. Hardin_ Jun 12 2012