Roman Numerals -- from Wolfram MathWorld
https://mathworld.wolfram.com/RomanNumerals.html
WEBIn particular, instead of using four symbols to represent a 4, 40, 9, 90, etc. (i.e., IIII, XXXX, VIIII, LXXXX, etc.), such numbers are instead denoted by preceding the symbol for 5, 50, 10, 100, etc., with a symbol indicating subtraction. For example, 4 …
DA: 23 PA: 1 MOZ Rank: 44