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 A203180 #7 Jul 22 2025 17:02:55 %S A203180 5,18,235,2466,23083,223567,2208945,22411843,216858412,2141041521, %T A203180 21294389765,209517628754,2070288232686,20420464639642, %U A203180 201913230471755,1993188902599209,19665745111235770,194376407794905718 %N A203180 Number of nX7 0..2 arrays with every 1 immediately preceded by 0 to the left or above, no 0 immediately preceded by a 0, and every 2 immediately preceded by 0 1 to the left or above. %C A203180 Column 7 of A203181 %H A203180 R. H. Hardin, <a href="/A203180/b203180.txt">Table of n, a(n) for n = 1..210</a> %e A203180 Some solutions for n=5 %e A203180 ..0..1..2..0..1..0..1....0..1..0..1..2..0..1....0..1..0..1..2..0..1 %e A203180 ..1..0..1..2..0..1..0....1..0..1..2..0..1..0....1..0..1..0..1..2..0 %e A203180 ..0..1..0..1..1..2..1....0..1..0..1..1..0..1....0..1..0..1..2..0..1 %e A203180 ..1..0..1..0..1..0..1....1..0..1..0..2..1..2....1..2..1..2..0..1..0 %e A203180 ..0..1..2..1..0..1..0....2..1..0..1..2..0..1....0..1..0..1..1..0..1 %K A203180 nonn %O A203180 1,1 %A A203180 _R. H. Hardin_ Dec 30 2011