cp's OEIS Frontend

A352623 a(n) is the maximum number k of queens that can be placed on an n X n chessboard such that, for each number j in 0..k-1, there is a queen attacking exactly j unoccupied squares.

%I A352623 #52 Apr 10 2022 10:04:12
%S A352623 0,1,0,5,8,11,14,18,22
%N A352623 a(n) is the maximum number k of queens that can be placed on an n X n chessboard such that, for each number j in 0..k-1, there is a queen attacking exactly j unoccupied squares.
%C A352623 On the 6 X 6 board in the illustration (see Example), each square containing a number is occupied by a queen, and the number in that square is the number of unoccupied squares attacked by that queen. (Each square with no number is unoccupied.)
%C A352623 Solvers:
%C A352623 a(4) = 8 by Rodolfo Kurchan
%C A352623 a(5) = 11 by Gustavo Piñeiro
%C A352623 a(6) = 14 by Antonio Misericordia
%C A352623 a(7) = 18 by Antonio Misericordia
%C A352623 a(8) = 22 by Giorgio Vecchi
%H A352623 Rodolfo Kurchan, <a href="https://www.puzzlefun.online/chess-puzzle-fun-05">Chess Puzzle Fun 5 Uneven Attacks</a>
%e A352623 Solution illustrating a(6) = 14 by Antonio Misericordia:
%e A352623   +---+---+---+---+---+---+
%e A352623   | 2 | 7 |   | 5 | 4 | 0 |
%e A352623   +---+---+---+---+---+---+
%e A352623   | 10|   |   |   | 6 | 1 |
%e A352623   +---+---+---+---+---+---+
%e A352623   |   |   |   | 11|   | 3 |
%e A352623   +---+---+---+---+---+---+
%e A352623   |   |   |   | 13|   | 8 |
%e A352623   +---+---+---+---+---+---+
%e A352623   |   |   |   |   |   |   |
%e A352623   +---+---+---+---+---+---+
%e A352623   |   |   | 12|   | 9 |   |
%e A352623   +---+---+---+---+---+---+
%Y A352623 Cf. A186238.
%K A352623 nonn,more
%O A352623 0,4
%A A352623 _Rodolfo Kurchan_, Mar 24 2022