72
72 is the atomic number of hafnium, and the number behind the finance shortcut known as the 'Rule of 72'.
- Even
- Composite
Where 72 fits
Why 72 is special
72's exceptionally high divisor count (12 divisors) is exactly what makes the Rule of 72 a practical mental-maths shortcut for compound-interest doubling times.
Same number, different meanings
How 72 is understood across different contexts — never implying one meaning because of another.
- Mathematics
72's exceptionally high divisor count (12 divisors) is exactly what makes the Rule of 72 a practical mental-maths shortcut for compound-interest doubling times.
- Science
72 is the atomic number of hafnium.
- Finance & economics
The 'Rule of 72' is a widely used finance shortcut: dividing 72 by an annual interest-rate percentage gives an approximate number of years for an investment to double through compound growth.
Factors & digit properties
- Divisors (12)
- 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72
- Prime factorisation
- 2^3 × 3^2
- Digit sum
- 9
- Digital root
- 9
Representations
- Decimal
- 72
- Binary
- 1001000
- Octal
- 110
- Hexadecimal
- 48
- Roman numeral
- LXXII
- Scientific notation
- 7.200 × 10^1
Other mathematical patterns
- Abundant number
- Powerful number
- Harshad (Niven) number
Related numbers & connections
36 is a factor of 72 (36 × 2 = 72).
View 36 →Mathematically related
- has factor36
why?
Strength 0.50, confidence "high".
Science
72 is the atomic number of hafnium.
DocumentedScience
Finance & economics
The 'Rule of 72' is a widely used finance shortcut: dividing 72 by an annual interest-rate percentage gives an approximate number of years for an investment to double through compound growth.
Widely documentedFinance & economics
Common questions
Is 72 a prime number?
No, 72 is not prime.
What are the factors of 72?
The factors of 72 are 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72.
What is 72 in Roman numerals?
72 in Roman numerals is LXXII.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026