Question 24
How many four-digit positive integers $abcd,$ with $a \neq 0,$ have the property that the three two-digit integers $ab < bc < cd$ form an increasing arithmetic sequence?
One such number is $4692,$ where $a=4,$ $b=6,$ $c=9,$ and $d=2.$
One such number is $4692,$ where $a=4,$ $b=6,$ $c=9,$ and $d=2.$