by Danny Roth
Published June 2 2019 (link)
George and Martha are doing a mathematical crossword. There is a 3 x 3 grid with the numbers 1 to 9 inclusive appearing once each. The clues are as follows:
top line: a prime number
middle line: a prime number
bottom line: a prime number
left column: a perfect square
middle column: a perfect square
right column: a prime number
Although you do not need to know this, one of the diagonal three-digit numbers is also prime.
What is the sum of the three “across” numbers?