65
65 is the atomic number of terbium, and the smallest number expressible as the sum of two positive squares in two genuinely distinct ways (1² + 8² = 4² + 7² = 65).
- Odd
- Composite
Where 65 fits
Why 65 is special
65's dual-sum-of-squares property is a real, verifiable mathematical curiosity — not every number can be split that way even once, let alone twice.
Factors & digit properties
- Divisors (4)
- 1, 5, 13, 65
- Prime factorisation
- 5 × 13
- Digit sum
- 11
- Digital root
- 2
Representations
- Decimal
- 65
- Binary
- 1000001
- Octal
- 101
- Hexadecimal
- 41
- Roman numeral
- LXV
- Scientific notation
- 6.500 × 10^1
Other mathematical patterns
- Deficient number
- Semiprime
Related numbers & connections
13 is a factor of 65 (13 × 5 = 65).
View 13 →Mathematically related
- has factor13
why?
Strength 0.50, confidence "high".
Science
65 is the atomic number of terbium.
DocumentedScience
Mathematics
65 is the smallest number expressible as the sum of two positive squares in two genuinely distinct ways: 65 = 1² + 8² = 4² + 7².
DocumentedMathematics
Common questions
Is 65 a prime number?
No, 65 is not prime.
What are the factors of 65?
The factors of 65 are 1, 5, 13, 65.
What is 65 in Roman numerals?
65 in Roman numerals is LXV.
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