What is the factor tree for 1521?
Since the number is NOT even , then it will not divide by '2'
So try the next [ri,e number. which is '3'
Hence
3)1521 = 507
3)507 = 169
169 will not divde by '3,5, 7,11, but it will divide by '13' the next prime number.
13)169 = 13
13 = 1
So reduced to its factors it is is 3,3,13,13.