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 A213470 #11 Sep 07 2025 12:20:54 %S A213470 353,22506,615561,12773955,237475982,4198162231,72188618371, %T A213470 1220298706370,20395481622380,338170996357600,5574396540683306, %U A213470 91481580201645051,1496133943774251078,24401386122053197406,397092484505964837242,6450193163022177761972,104613879499273682174696 %N A213470 Number of 0..3 arrays of length 2*n+5 with sum less than 3*n in any length 2n subsequence (=less than 50% duty cycle). %H A213470 R. H. Hardin, <a href="/A213470/b213470.txt">Table of n, a(n) for n = 1..210</a> %e A213470 Some solutions for n=3: %e A213470 ..2....0....2....2....0....2....2....2....0....0....2....2....2....0....2....0 %e A213470 ..2....0....0....2....0....0....2....2....2....2....2....0....2....0....2....2 %e A213470 ..2....0....2....0....2....0....2....0....0....0....0....0....0....2....2....0 %e A213470 ..2....2....0....0....2....3....1....1....2....1....1....0....0....2....0....2 %e A213470 ..0....3....1....1....2....2....0....0....2....0....0....1....2....0....1....3 %e A213470 ..0....1....1....0....0....0....0....0....1....0....3....1....0....0....1....0 %e A213470 ..1....0....3....3....0....1....0....1....0....0....2....0....1....1....1....0 %e A213470 ..3....1....1....2....1....0....1....1....0....1....1....1....0....0....1....1 %e A213470 ..1....0....2....2....2....1....2....2....0....3....1....3....3....3....3....1 %e A213470 ..0....3....0....0....2....3....3....1....1....1....0....1....2....1....0....1 %e A213470 ..2....1....0....0....3....1....2....2....2....2....0....1....2....3....0....0 %Y A213470 Row 6 of A213464. %K A213470 nonn,changed %O A213470 1,1 %A A213470 _R. H. Hardin_, Jun 12 2012