4
4 is the smallest composite number, and is considered unlucky in Chinese, Japanese and Korean contexts.
Where 4 fits
Why 4 is special
4's mathematical simplicity (2²) contrasts with a well-documented, geographically specific unlucky association that Western tradition does not share.
4 connects to:
- beryllium — has scientific association with
- aspect ratio standard — appears in
- adult human skeleton — appears in
- time signature — appears in
- east asian cultures — is considered unlucky in
Same number, different meanings
How 4 is understood across different contexts — never implying one meaning because of another.
- Mathematics
4's mathematical simplicity (2²) contrasts with a well-documented, geographically specific unlucky association that Western tradition does not share.
- Science
4 is the atomic number of beryllium.
- Culture
In Mandarin, Cantonese and other Chinese varieties, 4 (四, sì) is a near-homophone of the word for 'death' (死), leading to widespread avoidance of the number in building floor numbering, phone numbers and gifts across Chinese-speaking, and to a lesser extent Japanese and Korean, contexts.
Not just a mathematical number
4is also used in ways where ordinary arithmetic doesn't apply — each listed below with what genuinely does and doesn't follow from it.
- Mathematical number
A genuine quantity — its mathematical properties (prime, square, factors, and so on) are real facts about it.
A genuine quantity that ordinary arithmetic applies to — it can be prime, even, a perfect square, added to another number meaningfully, and so on.
- Quantity
Also used as a quantity — Adult human skeleton.
A genuine count or amount of something — closest to a pure mathematical number, but tied to what's being counted (12 eggs is a genuine amount of eggs, not an abstract mathematical fact about the number 12).
4 in Numbers Around Us
4 is part of
Factors & digit properties
- Divisors (3)
- 1, 2, 4
- Prime factorisation
- 2^2
- Digit sum
- 4
- Digital root
- 4
Representations
- Decimal
- 4
- Binary
- 100
- Octal
- 4
- Hexadecimal
- 4
- Roman numeral
- IV
- Scientific notation
- 4.000 × 10^0
Other mathematical patterns
- Palindromic number
- Deficient number
- Powerful number
- Highly composite number
- Narcissistic (Armstrong) number
- Semiprime
- Harshad (Niven) number
- Lucas number
Related numbers & connections
4 is the atomic number of beryllium.
The classic television and early-cinema aspect ratio is 4:3.
4 is considered unlucky in Chinese, Japanese and Korean contexts due to a homophone with 'death'.
Scientific association
- has scientific association withBeryllium (chemical element)
why?
Strength 0.50, confidence "high".
Numbers Around Us
- appears inAspect ratio standards
why?
Strength 0.50, confidence "high".
- appears inAdult human skeleton
why?
Strength 0.50, confidence "high".
- appears inMusical time signatures
why?
Strength 0.50, confidence "high".
Culturally related
- is considered unlucky inChinese-, Japanese- and Korean-speaking contexts
why?
Strength 0.50, confidence "high".
Science
4 is the atomic number of beryllium.
DocumentedScience4 is the atomic number of beryllium.
DocumentedScience
Culture
In Mandarin, Cantonese and other Chinese varieties, 4 (四, sì) is a near-homophone of the word for 'death' (死), leading to widespread avoidance of the number in building floor numbering, phone numbers and gifts across Chinese-speaking, and to a lesser extent Japanese and Korean, contexts.
Widely documentedCultureCulture: Chinese, Japanese and KoreanGeography: East Asia
Common questions
Is 4 a prime number?
No, 4 is not prime.
What are the factors of 4?
The factors of 4 are 1, 2, 4.
What is 4 in Roman numerals?
4 in Roman numerals is IV.
Is 4 a lucky number?
4 is considered unlucky in Chinese-, Japanese- and Korean-speaking contexts — a documented cultural association, not a mathematical property.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 3 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026