Multiply it by any positive integer.
Delete the 0's in its decimal representation.

Beginning with any positive integer can we always obtain a single-digit number after a finite number of operations? For example, beginning with 7, we can multiply by 15 to obtain 105, delete the 0 to get 15, multiply by 2 to get 30, then delete the 0 to end with 3.

At two steps in the example there is a division by an integer rather than a multiplication.  Was the reference to "the first two steps" referring to the fact that after that is relies on division?

Posted by Charlie on 2019-09-10 12:47:44