Number of zeros in double factorial?

Question

Programming

Hello!
Who knows how to count the number of zeros in the Double Factorial Wikipedia ? There is a cool algorithm for counting the number of zeros in an ordinary factorial without calculating the factorial itself - Super Algorithm . how to use it in solving this problem?

Answer 1

The solution is rather trivial:
for odd n -> n!! odd, i.e. no zeros at the end.
for even - in the "super-duper" algorithm, replace 5 with 10 (and powers of ten), since there are no fives (odd factors) there at all.