A308890 Follow along the squares in the square spiral (as in A274640); in each square write the smallest positive number that a knight placed at that square cannot see.

1, 1, 1, 1, 2, 2, 2, 3, 3, 2, 2, 2, 2, 3, 3, 2, 3, 4, 4, 3, 1, 2, 4, 3, 2, 1, 4, 4, 4, 3, 1, 2, 4, 4, 2, 1, 1, 1, 4, 4, 1, 1, 1, 3, 2, 4, 4, 1, 1, 1, 3, 3, 4, 3, 1, 1, 1, 3, 2, 4, 4, 2, 3, 1, 2, 1, 2, 2, 2, 2, 1, 2, 2, 3, 3, 2, 4, 3, 2, 1, 2, 2, 2, 3, 2, 2, 2, 2, 1, 2, 2, 3, 3, 2, 1

Offset: 1

Author

N. J. A. Sloane, Jul 01 2019

Keywords

• nonn

Comments

Similar to A274640, except that here we consider the mex of squares that are a knight's moves rather than queen's moves.

Since there are at most 4 earlier cells in the spiral at a knight's move from any square, a(n) <= 5.

This is obtained by adding 1 to the terms of A308884. "Mex" here means minimal positive excluded value.

Crossrefs

Cf. A247640, A274641, A308885-A308895.