If an integer n is written as a product of prime numbers, this product (known as its
prime factorization) can be used to determine the number of positive factors of n. For
example, the prime factorization of 28 = 2 × 2 × 7 = 22 × 7
1
. The positive factors of 28
are:
28 = 22 × 7
1
14 = 21 × 7
1
7 = 20 × 7
1
4 = 22 × 7
0
2 = 21 × 7
0
1 = 20 × 7
0
Each positive factor includes 2, 1 or 0 twos, 1 or 0 sevens, and no other prime numbers.
Since there are 3 choices for the number of twos, and 2 choices for the number of sevens,
there are 3 × 2 = 6 positive factors of 28.
(a) How many positive factors does 675 have?
(b) A positive integer n has the positive factors 9, 11, 15, and 25 and exactly fourteen
other positive factors. Determine the value of n.
(c) Determine the number of positive integers less than 500 that have the positive
factors 2 and 9 and exactly ten other positive factors.
If an integer n is written as a product of prime numbers, this product (known as its
prime factorization) can be used to determine the number of positive factors of n. For
example, the prime factorization of 28 = 2 × 2 × 7 = 22 × 7
1
. The positive factors of 28
are:
28 = 22 × 7
1
14 = 21 × 7
1
7 = 20 × 7
1
4 = 22 × 7
0
2 = 21 × 7
0
1 = 20 × 7
0
Each positive factor includes 2, 1 or 0 twos, 1 or 0 sevens, and no other prime numbers.
Since there are 3 choices for the number of twos, and 2 choices for the number of sevens,
there are 3 × 2 = 6 positive factors of 28.
(a) How many positive factors does 675 have?
(b) A positive integer n has the positive factors 9, 11, 15, and 25 and exactly fourteen
other positive factors. Determine the value of n.
(c) Determine the number of positive integers less than 500 that have the positive
factors 2 and 9 and exactly ten other positive factors.