A positive integer k is called a "lucky" number if the units digit of k^4 is 6. How many lucky numbers smaller than 10 are there?
14 = 1
24 = 16
34 = 81
44 = 256
54 = 625
64 = 1,296
74 = 2,401
84 = 4,096
94 = 6,561 Looks like there are 4 of them.
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