220
220 and 284 are the smallest pair of amicable numbers.
- Even
- Composite
Where 220 fits
Why 220 is special
The divisors of 220 add up to 284, and the divisors of 284 add up to 220. The pair was known to the Pythagoreans and carried into medieval talismans as a symbol of friendship — a documented historical use, distinct from any claim that the property means anything.
Factors & digit properties
- Divisors (12)
- 1, 2, 4, 5, 10, 11, 20, 22, 44, 55, 110, 220
- Prime factorisation
- 2^2 × 5 × 11
- Digit sum
- 4
- Digital root
- 4
Representations
- Decimal
- 220
- Binary
- 11011100
- Octal
- 334
- Hexadecimal
- dc
- Roman numeral
- CCXX
- Scientific notation
- 2.200 × 10^2
Other mathematical patterns
- Abundant number
- Harshad (Niven) number
Related numbers & connections
The smallest amicable pair: each number's proper divisors sum to the other. Known to the Pythagoreans and unmatched by any second pair for over a thousand years.
View 284 →The two smallest amicable pairs. Euler produced dozens of larger pairs while missing 1,184 and 1,210, which a sixteen-year-old found in 1866.
View 1184 →Mathematics
The proper divisors of 220 sum to 284 and those of 284 sum back to 220. The Pythagoreans knew the pair, and it appears in medieval talismans as a symbol of friendship — a documented historical use, which is a different claim from the property meaning anything.
DocumentedMathematics
Common questions
Is 220 a prime number?
No, 220 is not prime.
What are the factors of 220?
The factors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55, 110, 220.
What is 220 in Roman numerals?
220 in Roman numerals is CCXX.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 1 reviewer-confirmed record, sourced and reviewed before publication.
Last reviewed: 3 August 2026