XXI
20 + 1 = 21
XXI breaks down as XX + I (XX = 20, I = 1), which add up to 21.
XXI breaks down as XX + I (XX = 20, I = 1), which add up to 21.
The number 21 is written XXI in Roman numerals. Roman numerals use seven letters — I (1), V (5), X (10), L (50), C (100), D (500) and M (1000) — combined from largest to smallest, with subtractive pairs such as IV (4) and IX (9). Need another number? Use the Roman numeral converter or see the 1–100 chart.