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Question

The largest $n \in N$ such that $3^n$ divides $50!$ is :

The correct answer is
22

Largest n: Power of 3 Divides 50!

The problem requires finding the highest power of 3 that divides $50!$. We use Legendre's Formula to determine the exponent of a prime $p$ in the factorization of $m!$.

Legendre's Formula

The formula is given by:

$ E_p(m!) = \sum_{k=1}^{\infty} \lfloor \frac{m}{p^k} \rfloor $

Here, $m = 50$ and the prime $p = 3$. We need to calculate $E_3(50!)$.

Exponent Calculation Steps

Calculate the terms of the sum:

  • $ \lfloor \frac{50}{3^1} \rfloor = \lfloor \frac{50}{3} \rfloor = 16 $
  • $ \lfloor \frac{50}{3^2} \rfloor = \lfloor \frac{50}{9} \rfloor = 5 $
  • $ \lfloor \frac{50}{3^3} \rfloor = \lfloor \frac{50}{27} \rfloor = 1 $
  • $ \lfloor \frac{50}{3^4} \rfloor = \lfloor \frac{50}{81} \rfloor = 0 $

Subsequent terms will also be 0 since $3^k$ exceeds 50.

Total Exponent Value

Sum the results from the steps:

$ n = E_3(50!) = 16 + 5 + 1 + 0 = 22 $

Therefore, the largest integer $n$ for which $3^n$ divides $50!$ is 22.

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