Question 178
How many 4-digit numbers $ABCD$ are there with the property that
$$
|A - B| = |B - C| = |C - D|?
$$
Note that the first digit $A$ of a four-digit number $ABCD$ cannot be zero.
$$
|A - B| = |B - C| = |C - D|?
$$
Note that the first digit $A$ of a four-digit number $ABCD$ cannot be zero.