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 A209680 #10 Jul 22 2025 21:53:56 %S A209680 1,15,1508,6716352,66825091608,16894558898454012, %T A209680 7697358649459140517788,87677668153076602430717324907, %U A209680 1797666180378975423054345009058355238,921444360078430965633564486047727718449222837 %N A209680 Number of n X n 0..5 arrays with every element equal to a diagonal or antidiagonal reflection, and new values 0 upwards introduced in row major order. %C A209680 Column 4 of A209684 %H A209680 R. H. Hardin, <a href="/A209680/b209680.txt">Table of n, a(n) for n = 1..48</a> %e A209680 Some.solutions.for.n=3 %e A209680 ..0..0..1....0..0..1....0..1..2....0..1..1....0..1..1....0..1..1....0..0..1 %e A209680 ..2..1..0....0..1..2....1..1..1....1..1..0....1..2..3....1..2..3....0..0..1 %e A209680 ..1..2..0....2..2..1....0..1..1....1..0..1....1..3..1....1..3..0....2..1..0 %K A209680 nonn %O A209680 1,2 %A A209680 _R. H. Hardin_ Mar 11 2012