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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.

A208865 Number of n X n 0..3 arrays with new values 0..3 introduced in row major order and no element equal to more than one of its immediate leftward or upward or right-upward antidiagonal neighbors.

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%I A208865 #8 Jul 22 2025 21:32:22
%S A208865 1,12,6520,52947540,5134914951163,5935974611645510227,
%T A208865 81798476241280856702695038,13436627707296496011221331402032076,
%U A208865 26310300796694291418752809230234516335649298
%N A208865 Number of n X n 0..3 arrays with new values 0..3 introduced in row major order and no element equal to more than one of its immediate leftward or upward or right-upward antidiagonal neighbors.
%C A208865 Diagonal of A208872
%e A208865 Some solutions for n=4
%e A208865 ..0..1..0..0....0..0..0..1....0..0..0..0....0..1..1..1....0..0..0..1
%e A208865 ..2..0..3..0....1..1..2..0....1..1..1..2....0..0..0..1....1..2..2..0
%e A208865 ..2..0..3..1....0..1..1..3....2..0..1..3....1..1..0..0....1..3..1..3
%e A208865 ..1..2..0..2....3..0..3..1....1..3..0..1....0..1..1..1....1..0..3..0
%K A208865 nonn
%O A208865 1,2
%A A208865 _R. H. Hardin_ Mar 02 2012

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