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 A335445 #62 Jan 21 2024 09:36:45 %S A335445 1,4,8,13,21,28,37,50 %N A335445 Maximum number of rooks within an n X n chessboard, where each rook has a path to an edge. %C A335445 The puzzle can be visualized on an n X n chessboard. The goal is to maximize the number of rooks within the chessboard that can leave the grid without requiring another rook to move. An example invalid chessboard for a(3): %C A335445 XXX %C A335445 XXX %C A335445 XXX %C A335445 Here, the top and bottom rows of rooks can leave the chessboard. The middle row is invalid as the middle rook would not be able to leave the chessboard without one of the surrounding rooks having to move. A valid example chessboard for a(3): %C A335445 XXX %C A335445 X.X %C A335445 XXX %C A335445 Here, all rooks have free access to the outside of the grid. %C A335445 This game is isomorphic to the Ship City problem proposed by Ilmer. %H A335445 V. Ilmer, <a href="https://veniamin-ilmer.github.io/ship-city">Ship City</a>. %H A335445 Nicholas Tran, <a href="https://github.com/NicholasACTran/ship-city">Solution in ASP</a>. %e A335445 For n = 2, an example maximal solution is: %e A335445 XX %e A335445 XX %e A335445 For n = 4, an example maximal solution is: %e A335445 XXXX %e A335445 XXX. %e A335445 ..XX %e A335445 XXXX %K A335445 nonn,hard,more %O A335445 1,2 %A A335445 _Nicholas Tran_, Jul 14 2020