Four numbers have been given out of which three are alike in some manner, while one is different. Choose the odd one.

15 21 33 42

42

Except option (4), all are product of 3 and prime number. Option 1: (3 × 5) = 15 Option 2: (3 × 7) = 21 Option 3: (3 × 11) = 33 Option 4: (3 × 14) = 42