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 A212473 #6 Jun 02 2025 07:58:26 %S A212473 30,486,7862,126606,2034200,32644314,523487828,8390738062, %T A212473 134446993320,2153764911576,34495886876214,552428007496418, %U A212473 8845775486728392,141630619844515292,2267494906950636872,36300174404152871822 %N A212473 Number of 0..3 arrays of length 2*n+1 with sum no more than 3*n in any length 2n subsequence (=50% duty cycle). %C A212473 Row 2 of A212471 %H A212473 R. H. Hardin, <a href="/A212473/b212473.txt">Table of n, a(n) for n = 1..210</a> %e A212473 Some solutions for n=3 %e A212473 ..0....2....2....2....0....1....0....1....0....0....2....2....1....3....0....0 %e A212473 ..0....0....0....0....0....1....3....1....0....1....2....0....0....0....1....1 %e A212473 ..2....3....2....1....2....0....0....0....1....1....3....0....1....0....1....3 %e A212473 ..1....3....3....0....0....3....1....0....1....3....0....1....0....0....0....0 %e A212473 ..2....0....1....3....1....2....2....1....1....0....0....1....1....1....0....3 %e A212473 ..0....0....1....1....2....2....1....3....2....0....1....0....0....2....1....0 %e A212473 ..2....0....2....1....2....1....2....0....1....0....1....0....0....0....2....2 %K A212473 nonn %O A212473 1,1 %A A212473 _R. H. Hardin_ May 17 2012