Question 1137641
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The units digit of numbers 64, 64^2, 64^3, 64^4, 64^5  and so on form the cyclic sequence 4, 6, 4, 6, 4 . . . . and so on.


The length of the cycle is 2; each even-indexed number in this cycle is 6; each odd-indexed number in this cycle is 4.


So, the answer to the problem's question is 4  (since the degree index 401 is an odd number).
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Solved and explained.