Observe the grid below. The blank squares should be filled with whole numbers between 1 and 20 inclusive. Any of the numbers may occur more than once, or not at all.
The numbers in every horizontal row add up to the number totals on the right in bold type, as do the long diagonal lines (summing 88 top right and 122 bottom right). Those in every vertical column sum to the numbers in bold type along the bottom.
So. What are the missing numbers?