This is a question of probability. First of all, the first digit has 9 digits to choose from (0-9 divided by 1), the third digit also has 9 digits to choose from (0-9 divided by 7), and the fifth digit is odd, so only the five digits 1, 3, 5, 7 and 9 can be selected. So if you want to get it, you have to get 9x9x5=405 times, and the probability should be.