A396187 Consider the square spiral with its cells numbered starting at 0, as in A308884 and A274641. Two players, Black and Red, take turns. When it is Black's turn, he places a knight at the first cell in the spiral that is beyond the last Red knight and is not attacked by any Red knight, and when it is Red's turn, she places a knight at the first cell that is beyond the last Black knight and is not not attacked by any Black knight. Sequence lists squares not occupied by a knight.

4, 8, 9, 10, 11, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 26, 27, 28, 30, 31, 32, 33, 34, 38, 39, 43, 44, 46, 50, 52, 53, 57, 58, 60, 65, 66, 73, 74, 76, 78, 80, 82, 83, 84, 86, 87, 88, 89, 94, 96, 97, 98, 99, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 116, 118, 119, 123, 124, 126, 128, 129, 130, 131, 132

Offset

0,1

References

Ingmar Eissfeldt, Email to N. J. A. Sloane, May 15 2026.

Links

N. J. A. Sloane, Table of n, a(n) for n = 0..19999

Michael S. Branicky, Python program for OEIS A396185, A396186 and A396187

Crossrefs

Cf. A274641, A308884, A392177, A392178, A396185, A396186.

Sequence in context: A312828 A267647 A362453 * A214489 A189207 A127162

Adjacent sequences: A396184 A396185 A396186 * A396188 A396189 A396190

Keyword

nonn

Author

N. J. A. Sloane, May 31 2026, based on an email from Ingmar Eissfeldt, May 15 2026.

Status

approved