What five numbers are found only once in a multiplication table?

Answer 1

It would depend on how the multiplication table is formatted, but assuming that you don't have any 1x columns or rows - so you start with 2x2 and go up to 12x12, then the numbers which are squares of prime numbers will appear only once: 2², 3², 5², 7², and 11², or {4, 9, 25, 49 and 121}.

• The only way you can get 4 is 2 x 2, or 1 x 4 or 4 x 1;
• 9 is 3 x 3 or 1 x 9 or 9 x 1, etc.

So if there is no 1x column/row, then those numbers will appear only one time.