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 A265921 #6 Apr 20 2020 19:38:56 %S A265921 5,340,17936,542940,8821464,112139348,1135042936,15078628680, %T A265921 249568483336,2294594493868,25866958553904 %N A265921 Number of n X n 0..4 arrays with the absolute differences of each element with its with horizontal and antidiagonal neighbors unique. %C A265921 Diagonal of A265928. %e A265921 Some solutions for n=3 %e A265921 ..3..1..4....1..1..4....0..4..3....3..1..1....2..4..3....0..1..1....0..4..3 %e A265921 ..2..4..1....3..0..2....1..1..4....4..3..3....0..3..1....3..0..2....2..3..0 %e A265921 ..0..3..4....1..3..0....0..4..3....0..0..4....4..1..3....4..1..3....1..0..4 %Y A265921 Cf. A265928. %K A265921 nonn %O A265921 1,1 %A A265921 _R. H. Hardin_, Dec 18 2015