5; 1; 4 or 63.
7, 9, 3, 1 to the nth power 7, 10 divided by the cycle of 4 and 2, so the unit is 9,
3, 9, 7, 1, 15 divided by 4 is greater than 3, so the unit is 7.
Of course, the twentieth power of 2 is 6 and 20 is a multiple of 4.
The n power of 5 is 5. So the unit bit is 9*7*6*5, because 9*7*6 is an even number, and even *5 bits must be 0, so the unit bit.
It's 0