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 A338289 #14 Oct 24 2020 07:04:49 %S A338289 1,12,9,4,7,18,35,14,29,32,55,28,13,34,17,40,21,46,25,50,79,26,47,76, %T A338289 43,70,105,148,65,98,37,62,33,30,53,84,49,52,87,56,59,92,89,58,91,130, %U A338289 57,88,127,174,229,122,167,82,119,78,115,160,75,72,107,150,201,104,147,144,193,140,95,136,185,132,135,184,181 %N A338289 Squares visited by the black knight when a white knight and a black knight are moving on a spirally numbered board, always to the lowest available unvisited square; white moves first. %C A338289 Board is numbered with the square spiral: %C A338289 17--16--15--14--13 . %C A338289 | | . %C A338289 18 5---4---3 12 . %C A338289 | | | | . %C A338289 19 6 1---2 11 . %C A338289 | | | . %C A338289 20 7---8---9--10 . %C A338289 | . %C A338289 21--22--23--24--25--26 %C A338289 Both knights start on square 1, white moves to the lowest unvisited square (10), black then moves to the lowest unvisited square (12) and so on... %C A338289 This sequence is finite, on the black knight's 1879th step, square 4242 is visited, after which there are no unvisited squares within one knight move. %C A338289 The sequences generated by 4 knights and 8 knights also produce new sequences not yet in the OEIS. %H A338289 N. J. A. Sloane and Brady Haran, <a href="https://www.youtube.com/watch?v=RGQe8waGJ4w">The Trapped Knight</a>, Numberphile video (2019) %Y A338289 Cf. A338288, A338290. %K A338289 nonn,fini %O A338289 1,2 %A A338289 _Andrew Smith_, Oct 20 2020