Problem:
How many sequences of 5 positive integers satisfy ?
Problem:
How many sequences of 5 positive integers satisfy ?
Solution:
We count based on how many 's the sequence contains.
If then this gives us possibility.
If and , can be . Each such sequence can be arranged in different ways, for a total of ways in this case.
If three of the numbers are , the last two can be , or . Counting ordering, this gives a total of possibilities.
If two of the numbers are , the other three must be equal to for the product to be under , and this yields more possibilities.
Thus there are such sequences.