Math Problem Statement

Consider the product: 1 × 2 × 3 × 4 × ... × 30. Determine the largest value of k such that 2^k is a factor of this product.

Solution

The problem asks to determine the largest value of kk such that 2k2^k is a factor of the product 1×2×3××301 \times 2 \times 3 \times \cdots \times 30, which is the factorial 30!30!.

To find the largest value of kk for which 2k2^k divides 30!30!, we need to count how many factors of 2 are in 30!30!. This can be done by using Legendre's formula, which states that the exponent of a prime pp in n!n! is given by:

k=np+np2+np3+k = \left\lfloor \frac{n}{p} \right\rfloor + \left\lfloor \frac{n}{p^2} \right\rfloor + \left\lfloor \frac{n}{p^3} \right\rfloor + \cdots

Here, n=30n = 30 and p=2p = 2. Let's calculate kk:

k=302+304+308+3016+3032k = \left\lfloor \frac{30}{2} \right\rfloor + \left\lfloor \frac{30}{4} \right\rfloor + \left\lfloor \frac{30}{8} \right\rfloor + \left\lfloor \frac{30}{16} \right\rfloor + \left\lfloor \frac{30}{32} \right\rfloor

Now, evaluating each term:

302=15\left\lfloor \frac{30}{2} \right\rfloor = 15 304=7\left\lfloor \frac{30}{4} \right\rfloor = 7 308=3\left\lfloor \frac{30}{8} \right\rfloor = 3 3016=1\left\lfloor \frac{30}{16} \right\rfloor = 1 3032=0\left\lfloor \frac{30}{32} \right\rfloor = 0

Thus, the total kk is:

k=15+7+3+1=26k = 15 + 7 + 3 + 1 = 26

So, the largest value of kk such that 2k2^k is a factor of 30!30! is 26.

Would you like a detailed breakdown or further clarification?


Here are five related questions for practice:

  1. What is the largest kk such that 2k2^k divides 50!50!?
  2. How would you find the largest kk such that 3k3^k divides 30!30!?
  3. Can you calculate the number of factors of 5 in 30!30!?
  4. What is the sum of the factors of 2 in the factorial of any number n!n!?
  5. How would this approach change if the prime pp was 7 instead of 2?

Tip: Legendre's formula is a powerful tool for finding the highest powers of any prime that divide a factorial.

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Math Problem Analysis

Mathematical Concepts

Number Theory
Factorials
Prime Factorization

Formulas

Legendre's formula for finding the power of a prime in a factorial

Theorems

Legendre's theorem

Suitable Grade Level

Grades 9-12