Question Details

The largest nβˆˆπ‘, for which 7𝑛 divides 101 ! is

Options

A

16

B

18

C

19

D

15

Show Answer

Correct Answer :

Option A

16

Solution :

The correct option is 16.


To find the largest natural number n such that 7n divides 101!, we need to find the exponent of the prime number 7 in the prime factorization of 101! (101 factorial).


We can use Legendre's formula to calculate the highest power of a prime p that divides n!. The formula is given by:

E ( p ) = ⌊ n p βŒ‹ + ⌊ n p 2 βŒ‹ + ⌊ n p 3 βŒ‹ + …


Here, n=101 and p=7. Let's compute each term step-by-step:

1. First power of 7:
⌊ 101 7 βŒ‹ = ⌊ 14.428 βŒ‹ = 14

2. Second power of 7 (72=49):
⌊ 101 49 βŒ‹ = ⌊ 2.061 βŒ‹ = 2

3. Third power of 7 (73=343):
⌊ 101 343 βŒ‹ = 0


Now, summing up these values to find the total exponent n:

n = 14 + 2 + 0 = 16


Thus, the largest natural number n for which 7n divides 101! is 16.

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