Answer:
2^(1 + ((n-1) mod 4)) mod 10
Step-by-step explanation:
We presume you want the last digit of the power of 2, not the last digit of the exponent. Powers of 2 mod 10 are ...
2^0 : 1
2^1 : 2
2^2 : 4
2^3 : 8
2^4 : 6
2^5 : 2 . . . . and the sequence repeats: 2, 4, 8, 6, ...
That is, ...
(2^n) mod 10 = 2^(1 + ((n-1) mod 4)) mod 10 . . . for n > 0
