Well, I am really bored on my classes, so I started a game with my calculator. It was justly this same thing, with a subtraction between a number and his reverse. I have finished by finding a rule:

if the number is between 0 and 999:

find the difference between the first and the last number and multiply the result by 99. This will be the next number of the suite. You will finally arrive to 0.

ex: 743, 396, 297, 295, 495, 99, 0
(7-3)x99=396 ; (6-3)x99=297 ; (7-2)x99=495 ; (4-5)x99=0 ; (9-9)x99=0

It works for every number.

Next, if the number is between 1000 and 9999:

find the difference between the first 2 numbers and the 2 last (but read from right to left):

2345: 54-23 : 31
4598: 89-45 : 44
4231: 42-13 : 29

Next, multiply the dizens by 999 and the units by 90 and you will find the next number of the suite.:

2345: 54-23: 31 : (3x999 + 1 x 90) : 3087
2345-5432 : 3087

It works almost all the time. I'm actually trying to find the exception.

Finally, the infernal cycle (2178, 6524)

They occurs only when the difference between the firth two numbers and the last two (from right to left) is a palindrome:

4598, 4356, 2178, 6534, 2178, 6534...

4598 : 89-45 : 44 : a palindrome

And, pure coincidence, 4598 = 22x209. Every number that conducts to this cycle has at least one palindrome in his factors.

Finally, I have found this forum by typing in Google 2178 and 6534, because I wanted to know if someone else has found this before me.