What number does not belong 15 63 8 50?

Answer 1

Take your pick:

15 is the only number which is a product of 2 primes (3*5).

63 is the only number that is the products of three odd primes (3*3*7)

8 is the only cube number (22)

50 is the only number that is not one less than a square number (15=42-1, 63 = 82-1, 8 = 32-1).