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 A208461 #10 Feb 22 2025 14:35:14 %S A208461 1,15,20746,10318694804,4585512913250157737, %T A208461 3787532222733253394267947322830, %U A208461 10658767342117292737413813034097966371526603430 %N A208461 Number of n X n nonnegative integer arrays with new values 0 upwards introduced in row major order and no element equal to more than two of its immediate leftward or upward or right-upward antidiagonal neighbors. %e A208461 Some solutions for n=4: %e A208461 ..0..0..0..0....0..0..0..0....0..0..1..0....0..0..0..0....0..0..0..0 %e A208461 ..0..1..0..0....0..1..0..0....0..0..0..0....0..1..0..0....0..1..2..0 %e A208461 ..0..2..0..1....0..1..1..0....0..1..0..2....2..0..1..0....0..0..0..0 %e A208461 ..0..0..0..0....0..0..0..1....1..0..0..0....0..0..0..0....1..0..1..2 %Y A208461 Diagonal of A208466. %K A208461 nonn,more %O A208461 1,2 %A A208461 _R. H. Hardin_, Feb 27 2012