Customer number as prefix

I have problem with prefix name
it's list of my client and i would to sync id with customer number just like this:

Also it's my prefix:

So it means customer number 4 has: db4-* user4-* ftp4-*
but as you can see if i delete a client and add again it start with after last number so id 5 and C4 is different
but if i could use customer number as a prefix then i could solve this problem