Place the digits 1-6 in each row, column, and region. No orthogonally adjacent pair of cells, read as a two-digit number left-to-right or top-to-bottom, can be a prime number or a perfect square.
Place the digits 1-6 in each row, column, and region. No orthogonally adjacent pair of cells, read as a two-digit number left-to-right or top-to-bottom, can be a prime number or a perfect square.