If a number which is of the form ap×bq×..., where a,b,... are prime numbers and p,q,... are natural numbers, then the number of factors of the number is given by (p+1)x(q+1)x....
According to the question,
(p+1)×(q+i)×...=4=i×4=2×2
From the above equation, it can be concluded that the number in the given case can be of the form either a3 or a × b. There is only one number of the form a3 which is less than or equal to 15 i.e. 23. There are 4 numbers of the form a x b which are less than or equal to 15 and these numbers are 2 x 3, 2 x 5, 2 x 7 and 3 x 5 . Hence, the number of required numbers is 5.