GMAT Practice Question: For every even positive integer m, f(m) represents the product of all even integers from 2 to...
Question
For every even positive integer m, f(m) represents the product of all even integers from 2 to m, inclusive. For example, f(12)=2 4 6 8 10 12. What is the greatest prime factor of f(24) ?
- 23
- 19
- 17
- 13
- 11
Topics: number theory, prime factorization, odds/evens
Solution
Step 1
We factor each even term from 2 to 24 as 2 times an integer, then collect the powers of 2 and the remaining product.
f(24) = 24681012141618202224 =2^12(123456789101112) =2^1212!
Step 2
We break down 12! into prime powers to find its highest prime factor.
12! = 2^103^55^2711 The greatest prime factor is 11
Answer
11
