it was Ivan Zamorano who played with the number 1+8 at Inter Milan. Before Ronaldo came (and took his place) he wore the number 9. But as a "mathematical trick" he decided to wear the number 9 as a sum of 1+8 afterwards.
Zamorano officially had the number 18, but on the shirt they just printed it as 1+8.
Guess what happened if there were both numbers at the same time. Suddenly, there would have been numbers like 2x5 or 7+3 or 36:4 or 15-6 or 3^2 or ... ;-)