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 A321531 #11 Dec 14 2018 19:49:35 %S A321531 0,1,2,4,6,8,11,14,18,23 %N A321531 a(n) is the maximum number of distinct directions between n non-attacking rooks on an n X n chessboard. %C A321531 Directions are determined up to scaling and dihedral action of the square, as in (m,k)-riders. For example, the moves (1,2) and (2,-4) are considered to have the same direction. %e A321531 For n = 5, a 5 X 5 board with a(5) = 6 distinct directions is %e A321531 +---+---+---+---+---+ %e A321531 5| X | | | | | %e A321531 +---+---+---+---+---+ %e A321531 4| | | X | | | %e A321531 +---+---+---+---+---+ %e A321531 3| | | | X | | %e A321531 +---+---+---+---+---+ %e A321531 2| | | | | X | %e A321531 +---+---+---+---+---+ %e A321531 1| | x | | | | %e A321531 +---+---+---+---+---+ %e A321531 A B C D E %e A321531 Where the six distinct directions are: %e A321531 1) 1:4 by (A5,B1). %e A321531 2) 1:2 by (A5,C4). %e A321531 3) 2:3 by (A5,D3). %e A321531 4) 3:4 by (A5,E2). %e A321531 5) 1:3 by (B1,C4) and (B1,E2). %e A321531 6) 1:1 by (B1,D3), (C4,D3), (C4,E2), and (D3,E2). %Y A321531 Cf. A320448 (analogous with distance instead of direction). %K A321531 nonn,more %O A321531 1,3 %A A321531 _Peter Kagey_, Nov 12 2018