Hint: Work mod 10. In other words, think about the final digit of p. Every prime number apart from 2 and 5 ends with 1, 3, 7 or 9. What does that tell you about and ?
Hint: Work mod 10. In other words, think about the final digit of p. Every prime number apart from 2 and 5 ends with 1, 3, 7 or 9. What does that tell you about and ?
It tells me that for every prime apart from 2 and 5, either or is divisible by 5.