A set M of numbers is defined recursively by 2 and 3 belong

A set M of numbers is defined recursively by 2 and 3 belong to M If x and y belong to M. so does x * y Which of the following numbers belong to M? 6, 9, 16, 21, 26, 54, 72, 218

Solution

So M may contain following number :- 2,3,6,12,18,24,36,48,72,108,144,216,288.......so on....

Therefore

answer is:6,54,72

because there is no way M contains 9,21,26,218,16.