My apologies. There are three, not four, reversible components of 685.

There are only 95 numbers from 000 to 989 that are the sum of two, three-digit reversible numbers, i.e. about 9.6% of all the numbers. (989 is the largest three-digit number that can be decomposed into two reversible numbers.)

Of those that can be so decomposed, the first and last digit have a difference of zero or one and the middle digit is evenly divisible by two.

Hope this helps.

Michael Greaney