Kummer Arithmetic

Paul Erdös had another version of the story of how Kummer calculated 7 x 9.

Kummer said to himself: "Hmmm the product cannot be 61, because 61 is prime, it cannot be 65, because 65 is a multiple of 5, 67 is a prime, 69 is too big - Only 63 is left."

-- Paul Erdös' version