Answer:
123454321
Step-by-step explanation:
A palindrome word or number is a word or number that reads the same forwards and backwards, for example
"civic" and "level" are examples of 5-letter palindrome words.
1221 and 2332 are 4-digit palindrome numbers.
It is easy to construct a palindrome number; start from 1 and go increasing digits until reaching half the number, then go countdown.
For example
123454321 is an example of a 9-digit palindrome number.
There are infinite many of them.
