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 A187671 #7 Jul 22 2025 10:52:10 %S A187671 24,550,4044,17716,56080,150166,336776,702408,1330728,2385910,3973400, %T A187671 6550700,10068336,15247986,22545648,32579360,45246528,62983046, %U A187671 84524916,113900920,150370548,195521534,249456396,321513812,404142192,504603526 %N A187671 Number of 3X3 0..n arrays with each 2X2 subblock nonsingular and the array of 2X2 subblock determinants symmetric about the diagonal and antidiagonal. %C A187671 Row 2 of A187670 %H A187671 R. H. Hardin, <a href="/A187671/b187671.txt">Table of n, a(n) for n = 1..31</a> %e A187671 Some n=3 solutions for 3X3 %e A187671 ..3..3..3....2..1..3....0..1..0....2..1..1....1..0..3....3..0..2....2..3..1 %e A187671 ..0..1..0....2..0..2....2..1..2....2..2..0....0..3..2....0..1..2....1..0..1 %e A187671 ..3..0..3....0..1..0....2..2..2....2..1..1....3..3..3....2..0..3....2..3..2 %K A187671 nonn %O A187671 1,1 %A A187671 _R. H. Hardin_ Mar 12 2011