Number 21 in roman numerals

Converting number 21 to Roman numerals

Step 1:
 Remaining: 21
 Subtract: 10 (X)
 Current result: X 

Step 2:
 Remaining: 11
 Subtract: 10 (X)
 Current result: XX 

Step 3:
 Remaining: 1
 Subtract: 1 (I)
 Current result: XXI 

Basic Roman Numerals up to 3999

Basic Writing Rules

• It is forbidden to use more than three identical symbols in a row (exception - the letter M in classic notation)
• Subtraction is only possible for numbers that differ by 10 or 5:
• I is subtracted only from V and X (IV = 4, IX = 9)
• X is subtracted only from L and C (XL = 40, XC = 90)
• C is subtracted only from D and M (CD = 400, CM = 900)

Numbers Above 3999

Example of converting number 4,324:

 4,000 → ĪV̄ 300 → CCC 20 → XX 4 → IV 

Result: ĪV̄CCCXXIV

Historical Features

• In ancient Rome, various notations were used for large numbers
• The system using vinculum (horizontal line above) was standardized in the Middle Ages
• Sometimes double and triple vincula were used above to indicate multiplication by 1,000,000 and 1,000,000,000

Important Notes:

• The vinculum system allows for compact notation of very large numbers
• Not all fonts support symbols with macron
• In modern usage, numbers up to 3999 are most common
• When working with large numbers, it's important to consider the context of use and display capabilities