It is called a 28-digit number!
If your asking in a digit it's called a 4 digit number and it is the smallest 4 digit number
A digit is part of a number. the number 23 has two digits 2 and 3.
It is called a twelve-digit number. Its exact name will depend on the number.
There are none but the smallest 3 digit number is 161
A 22 digit number is called a quintillion.
I would just call it a "400-digit number".
Just that - a 26-digit number. There is no special name for that.
Calling it "17-digit number" is just fine.