As all the digits have to be present in the number hence repetition is not allowed such as 22222 or 33333 and so on.
Thousands and Units place can be taken by 3,5,7 meaning 3*2 ways = 6
Remaining positions can be taken by 2,4 and the remaining Odd digit - 3! ways = 6
thus total ways = 6*6 = 36.
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