Find the number of trailing zeroes in $20172017!!$

**
Notation:
**
$!!$
denotes the
double factorial function

The answer is 0.

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$\displaystyle 20172017!!=20172017\times20172015\times20172015\times20172013\times \cdots \times7\times5\times3\times1$

$\because$ All the numbers in the product are odd, like 20172017 , 20172015 , etc. and a number has trailing zeroes if it has both 2 and 5 as a factor but, $20172017!!$ doesn't has 2 as a factor

$\therefore$ There are no trailing zeroes.