Source: Mathematical Puzzles of Sam Loyd, Volume Two, edited by Martin Gardner, Dover Publications, New York, 1960, #155, #84, #48.
. x . x x x . . x x x x . x x . | Received from Kirk Bresniker, Igor Volkov (and Sam Loyd). There are 16 even rows. |
x . x . . . . . x . x . x x . . . . . . . . x x . x . x . . . . . x . x |
This is the only solution I've seen so far. Received from Rich Polster,
Philippe Fondanaiche Paris France, Igor Volkov (and Sam Loyd).
Several people made excellent attempts at this problem but forgot to check the off-diagonal directions (there were several answers with 3 checkers placed in a line of knight's moves, for example.) |
. . . . . x . x x . . x . . . . . . . . . x . x . x . x . . . . . . . . x . x . x x . . . . . . . . x . x . . . . . x . . . x . | This was received from Igor Volkov and is the same solution Sam Loyd gives. |