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 A212474 #6 May 02 2023 15:19:34 %S A212474 85,1597,27024,445780,7274268,118029501,1908601444,30794657082, %T A212474 496095308012,7983014938756,128351434757356,2062286003105664, %U A212474 33118464621596452,531627920798750598,8530886270887938488 %N A212474 Number of 0..3 arrays of length 2*n+2 with sum no more than 3*n in any length 2n subsequence (=50% duty cycle). %C A212474 Row 3 of A212471. %H A212474 R. H. Hardin, <a href="/A212474/b212474.txt">Table of n, a(n) for n = 1..210</a> %e A212474 Some solutions for n=3 %e A212474 ..0....0....1....2....2....0....2....2....1....2....1....1....1....2....0....3 %e A212474 ..0....0....2....0....0....0....2....0....0....1....1....0....0....1....1....0 %e A212474 ..1....2....1....1....1....1....1....3....2....0....0....1....0....2....3....2 %e A212474 ..0....1....0....1....3....2....0....0....2....0....0....0....3....0....0....0 %e A212474 ..2....1....0....0....2....1....0....1....2....0....1....0....0....0....0....1 %e A212474 ..2....0....1....1....1....0....3....1....0....1....2....2....0....0....0....1 %e A212474 ..1....2....3....3....2....3....3....2....0....2....3....1....3....0....3....2 %e A212474 ..1....2....1....2....0....2....0....0....1....2....3....2....1....3....0....2 %Y A212474 Cf. A212471. %K A212474 nonn %O A212474 1,1 %A A212474 _R. H. Hardin_, May 17 2012