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 A204623 #12 Jul 22 2025 18:10:31 %S A204623 12,96,768,6144,49152,393216,3145728,25165824,201326592,1610612736, %T A204623 12884901888,103079215104,824633720832,6597069766656,52776558133248, %U A204623 422212465065984,3377699720527872,27021597764222976,216172782113783808 %N A204623 Number of (n+1)X2 0..2 arrays with every 2X2 subblock having unequal diagonal elements or unequal antidiagonal elements, and new values 0..2 introduced in row major order. %C A204623 Column 1 of A204630 %H A204623 R. H. Hardin, <a href="/A204623/b204623.txt">Table of n, a(n) for n = 1..210</a> %F A204623 Empirical: a(n) = 8*a(n-1) %e A204623 Some solutions for n=3 %e A204623 ..0..0....0..0....0..0....0..0....0..1....0..0....0..0....0..0....0..0....0..1 %e A204623 ..0..1....1..2....0..1....0..1....2..1....1..1....0..1....0..1....0..1....1..1 %e A204623 ..2..2....0..2....0..1....1..2....2..0....2..0....1..1....0..0....2..1....1..2 %e A204623 ..0..2....2..1....0..1....2..2....0..1....0..1....1..2....2..1....0..2....1..2 %Y A204623 Cf. A094085, A270568. %K A204623 nonn %O A204623 1,1 %A A204623 _R. H. Hardin_ Jan 17 2012