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 A183681 #8 Jul 22 2025 09:09:09 %S A183681 6,32,256,3472,73344,2542368,140090240,12503757968,1787244586880, %T A183681 411927241028352,152442345546739968,90819596095626887104, %U A183681 86960426240537811217920,133963874202574308172821152 %N A183681 Number of (n+1)X(n+1) binary arrays with every 2X2 subblock nonsingular. %C A183681 Diagonal of A183688 %H A183681 R. H. Hardin, <a href="/A183681/b183681.txt">Table of n, a(n) for n = 1..19</a> %e A183681 Some solutions for 3X3 %e A183681 ..0..1..0....0..1..1....1..0..1....1..1..0....1..1..1....1..1..1....0..1..0 %e A183681 ..1..1..1....1..0..1....0..1..0....1..0..1....1..0..1....1..0..1....1..0..1 %e A183681 ..0..1..0....1..1..1....1..0..1....1..1..0....1..1..1....1..1..0....1..1..1 %K A183681 nonn %O A183681 1,1 %A A183681 _R. H. Hardin_ Jan 06 2011