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 A308897 #10 Jul 02 2019 11:05:22 %S A308897 1,2,1,2,3,4,1,3,4,2,3,4,1,3,4,2,5,6,7,8,1,5,6,7,8,2,5,6,7,8,1,5,6,7, %T A308897 8,2,3,6,5,8,7,4,1,3,6,5,8,7,4,2,3,6,5,8,7,4,1,3,6,5,8,7,4,2,9,10,11, %U A308897 12,13,14,15,16,1,9,10,11,12,13,14,15,16,2 %N A308897 Walk a rook along the square spiral numbered 1, 2, 3, ... (cf. A274640); a(n) = mex of earlier values the rook can move to. %C A308897 Mex here means "smallest positive missing number". %C A308897 Add 1 to the terms of A308896. %Y A308897 Cf. A274640, A308896. %K A308897 nonn %O A308897 1,2 %A A308897 _N. J. A. Sloane_, Jul 02 2019 %E A308897 More terms from _Rémy Sigrist_, Jul 02 2019