How many 6 digit numbers can be formed from013579?

Answer 1

Assuming you don't want a preceding zero, then:

~if~ you accept repeated use of the same digit (e.g. "111111"), then the answer is 5 * 65, or 38880

If digits can not be used repeatedly, then the answer is 5 * 5!, or 5 * 5 * 4 * 3 * 2 * 1, which equals 600.