Martin Gardner asked this in his Mathematical Games column in the September 1966 issue of Scientific American. William Cutler was the first of 24 readers who reduced the uncovered area to 49, using all but the 7x7 square. All the patterns were the same except for interchanging the squares of orders 17 and 18 and rearranging the squares of orders 1, ..., 6, 8, 9, and 10. Nobody proved that the solution is minimal.

| | | | | | | | | | | | 11 | | | | | | | | | 16 | | | | | +-----+--+----+ 22 | 21 | | | | 2| | | | | | 5 +--+----+ | | | | | | | |

  • ----------------+--+--+ 6 | | |

| | 3| | | | | ++-+-------+ | | | || | ++--------------------+ | || 8 +----------------------++ | | 18 || | | | | || | | | | ++---------+ | | | | | | 20 | | | 9 | | |

  • ------------------++ | 23 | |

| || | | | | ++----------+ | | | | | +---++---------------+ | | | | || | | 17 | 10 | | 4 || | | | +---------------+-------+---++ | | +-+---------+---------------+ | 15 | | | | | | | | | | | 12 | |

  • ------------------+-+ | +-+-------------+

| | | |1| | | | +------------+-+ | | | 24 | | | | | | | | | 19 | | 13 | 14 | | | | | | | | | | | | | | | |

  • --------------------+-------------------------+--------------+-------------+

lib/DbaDatabase.php:134: Warning: dba_replace() [<a href='function.dba-replace'>function.dba-replace</a>]: You cannot perform a modification to a database without proper access