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 A268450 #4 Feb 04 2016 21:59:02 %S A268450 2,9,61,581,7160,108032,1926444,39616567,922677334,24000231919, %T A268450 689530024294,21683683196634,740776505063512,27318331535557441, %U A268450 1081605306266896792,45759587251345781091,2060162120919764963754 %N A268450 Number of length-n 0..n arrays with no adjacent pair x,x+1 followed at any distance by x+1,x. %C A268450 Diagonal of A268457. %e A268450 Some solutions for n=6 %e A268450 ..0....3....1....3....5....3....6....1....6....3....1....2....2....5....1....3 %e A268450 ..1....0....1....5....3....1....6....4....3....6....2....2....3....0....1....5 %e A268450 ..3....6....2....1....5....5....4....2....3....6....2....1....1....1....2....5 %e A268450 ..6....1....6....1....5....4....3....5....0....2....0....5....6....4....4....1 %e A268450 ..1....2....4....2....3....1....1....5....2....0....1....5....3....2....0....0 %e A268450 ..3....6....4....2....3....6....2....1....0....0....1....1....4....1....4....1 %Y A268450 Cf. A268457. %K A268450 nonn %O A268450 1,1 %A A268450 _R. H. Hardin_, Feb 04 2016