CXXIII
Cmlxxxvii cxxiii cccxxi
123 = CXXIII
123
It is already in Hindu-Arabic numerals but if you mean in Roman numerals then it is written as: CXXIII
CXXIII
You can change it from 123 to 123/1. This is just how to write it on the computer usually. Otherwise, it will be: 123 1
123 is already in decimal form.
You write it as 123.
123
123%
123