What is the smallest value of n such that 2 0 5 0 ! is not divisible by 1 7 n ?
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I also did the same. @Atul Shivam You should change the ques to lowest possible value of n.
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Thanks. I've edited the problem accordingly.
That ingenious :)
Let m be the highest power of 1 7 which divides 2 0 5 0 ! .
m = ⌊ 1 7 2 0 5 0 ⌋ + ⌊ 1 7 2 2 0 5 0 ⌋ = 1 2 0 + 7 = 1 2 7
Therefore, the any value n > m will not divide 2 0 5 0 ! .
Answer = 1 2 8
Oops! I didn't notice your solution.
We just need to count the number of 17s in 2 0 5 0 ! . We can simplify the calculation by something like this -
n = 1 ∑ k ⌊ 1 7 n 2 0 5 0 ⌋
k must be equal to last n such that
⌊ 1 7 n 2 0 5 0 ⌋ > 0
After performing the calculations, we get the answer as 127. If 1 7 1 2 7 ∣ 2 0 5 0 ! then every smaller positive integral power less than 1 2 7 also divides 2 0 5 0 ! . Hence only 128 from the list doesn't divide 2 0 5 0 ! .
Simple standard approach.
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I cheated and solved this in a second: The answer must be the largest of the given choices, 1 2 8 ;)