9998
10000
9998
10001 and 9999, possibly.
Exactly as in the question 9999
9998
It is: XVIII = 18
It is 9998.
9998
It is: IX = 9
No, the roman numeral for 9999 would be (IX)CMXCIX. In written roman numerals the (IX) in parentheses would have a bar on top. This denotes multiplication of 1000.
If you mean Roman numeral then it is M = 1000