Math Problem Statement

solve

Let N = 1 × 2 × 3 × ... × n, where n is a positive integer. Find the largest possible value of n for which N is not divisible by some two-digit number.

Solution

This problem involves finding the largest integer nn for which the factorial N=1×2×3××nN = 1 \times 2 \times 3 \times \dots \times n is not divisible by any two-digit number. Let's analyze it.

For NN to be not divisible by any two-digit number, none of the prime factors of those two-digit numbers can fully divide NN. As nn grows, NN becomes divisible by an increasing number of factors, including two-digit numbers.

To solve this:

  1. Check divisibility for common two-digit primes: 11, 13, 17, 19, etc.
  2. The factorial N=n!N = n! will start becoming divisible by each of these primes when nn is greater than the largest two-digit number that each prime divides. Therefore, the solution is to identify the largest nn for which none of these primes divide n!n!.

Let's evaluate the answer choices:

Option Analysis

  1. 83: The factorial 83!83! will not include any multiples of some two-digit primes, meaning it could satisfy the requirement.
  2. 91 and higher**: By the time nn reaches 91 or higher, all two-digit primes will start to divide NN, as every two-digit number is included in the factorial by that point.

Thus, the largest value of nn for which N=n!N = n! is not divisible by some two-digit number is likely 83.

Answer:

The correct answer is A. 83.

Would you like further details or explanations on this?


  1. What happens to the divisibility if nn increases beyond 83?
  2. How do prime factors influence the divisibility of factorials?
  3. Why do factorials grow so quickly in terms of prime factors?
  4. Can we generalize this problem for three-digit numbers?
  5. How do non-prime factors affect the divisibility in factorials?

Tip: When solving divisibility problems, focus on prime factors to simplify analysis.

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Math Problem Analysis

Mathematical Concepts

Factorial
Divisibility
Prime Factorization

Formulas

Factorial N = n!
Divisibility Rules

Theorems

Prime Factor Divisibility

Suitable Grade Level

Grade 10-12