18 of them
The number 10 has a roman numeral of X. The number 50 has a roman numeral of L. These are the only 2 digit numbers with a single value.
There are 21 two-digit prime numbers.
A binary numeral system is system for representing numbers in which a radix of 2 is used - so that each digit in a binary numeral may have either of two different values.
There are five such numbers.
7 two-digit numbers.
There are zero numeral numbers in the word "Christ."
There are 2941 4-digit numbers such no two of its digits differ by 1.
36
There are 45 of them.
3
There are 90 two-digit numbers... starting with 10 and ending with 99.