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 A187420 #8 Jul 22 2025 10:43:37 %S A187420 175,1969,6512,44512,319792,2142214,13328138,88129302,580578920, %T A187420 3802787570,24886205614,163501852210,1072581861748,7032866591748, %U A187420 46126761827268,302624532393770,1985178392452142,13021958891247156 %N A187420 Number of (n+1)X3 0..2 arrays with every 2X2 subblock determinant equal to exactly one or two horizontal and vertical neighbor 2X2 subblock determinants. %C A187420 Column 2 of A187425 %H A187420 R. H. Hardin, <a href="/A187420/b187420.txt">Table of n, a(n) for n = 1..200</a> %e A187420 Some solutions for 5X3 %e A187420 ..1..1..1....2..0..2....1..2..1....2..1..0....2..1..0....1..1..0....1..2..1 %e A187420 ..2..1..0....2..2..2....0..1..1....1..1..1....0..1..2....2..2..0....0..0..0 %e A187420 ..1..1..1....0..2..0....0..1..1....2..1..0....0..1..2....0..2..2....1..2..1 %e A187420 ..2..2..2....0..0..0....1..1..1....2..1..2....0..1..2....1..2..1....1..1..0 %e A187420 ..0..0..0....2..0..0....1..0..0....0..0..2....2..1..0....1..2..1....0..2..2 %K A187420 nonn %O A187420 1,1 %A A187420 _R. H. Hardin_ Mar 09 2011