Find the smallest positive integer whose cube ends in 2017.
Please solve this fun problem.
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one can find x digit by digit, starting from the least significant one. If the least significant one is a 1
a 1 3 ≡ 7 ( m o d 1 0 ) ⟹ a 1 = 3
then, every time we find the j -th digit, we solve the equation
( 1 0 j a j + 1 + a j … a 1 ) 3 ≡ 2 0 1 7 m o d ( 1 0 j + 1 )
for a j + 1 . Note that you may expand the expression, that is taken to the power 3, in order to solve the equation.
the final result would be 9 0 7 3