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 A187706 #7 Jul 22 2025 10:53:36 %S A187706 128,1489,8272,31461,93476,235773,524284,1062857,1999212,3541677, %T A187706 5967404,9648841,15048584,22766353,33534080,48248321,67983232, %U A187706 94042589,127929948,171449249,226655576,295941137,382036240,488090685,617595596,774557293 %N A187706 Number of 3X3 0..n arrays with each 2X2 subblock off diagonal and antidiagonal nonsingular and the array of 2X2 subblock determinants antisymmetric about the diagonal and antidiagonal. %C A187706 Row 2 of A187705 %H A187706 R. H. Hardin, <a href="/A187706/b187706.txt">Table of n, a(n) for n = 1..33</a> %e A187706 Some n=3 solutions for 3X3 %e A187706 ..3..0..0....2..0..3....0..0..1....3..1..1....0..0..3....2..0..0....2..0..0 %e A187706 ..2..0..3....2..0..0....3..0..1....0..0..0....0..0..3....1..0..0....0..0..0 %e A187706 ..1..0..0....1..0..0....2..0..3....3..2..1....3..0..1....0..0..3....0..2..2 %K A187706 nonn %O A187706 1,1 %A A187706 _R. H. Hardin_ Mar 12 2011