Not all questions have one exact answer only. Check here some of them:
2 because it is the only even number
13 because it is the only two digit number
9 because it is the only number with a hole
2 because it is the only number where digit “3” does not appear in digital writing
9 because it is the only squared number
9 because it is the only not prime number
9 because it is the only number not included in the Fibonacci sequence
9 because it is the only number that has an even number of lines in digital writing
Can you find a criterion that would exclude number 3?
