Number analysis
65
65 is a composite odd number that factors as 5 × 13.
65 is a composite odd number that factors as 5 × 13.
The number itself
- Value
- 65
- Digits
- 2
- Digit sum
- 11
- Reversed
- 56
- Palindrome
- No
6 + 5
Digit sum repeated until one digit remains; equals n mod 9 (with 9 for multiples of 9).
Reverses to 56.
Parity and primality
- Parity
- Odd
- Prime
- No
- Prime factorisation
- 5 × 13
- Squarefree
- Yes
- Semiprime
- Yes
- Möbius μ(n)
- 1
- Nearest primes
- 61 ← → 67
Leaves remainder 1 on division by 2.
Composite — it factors as 5 × 13.
2 distinct prime factors, 2 with multiplicity.
No prime divides it twice.
A product of exactly two primes, counted with multiplicity.
(−1) to the power of 2 distinct prime factors.
A gap of 6 between them.
Divisors
- Aliquot sum
- 19
- Classification
- Deficient
1, 5, 13, 65
The proper divisors — everything except n itself.
Its proper divisors fall short by 46.
How many integers from 1 to n share no factor with n.
Sums and additive structure
- Sum of two squares
- Yes
- Sum of three squares
- Yes
- Sum of four squares
- Yes
- Sum of two cubes
- 1³ + 4³
1² + 8² = 65 · 4² + 7² = 65
Legendre's three-square theorem allows it.
Lagrange's four-square theorem: every non-negative integer is, without exception.
Shapes and sequences
- Figurate shapes
- None
Not triangular, square, pentagonal, hexagonal, cubic, Fibonacci, Lucas, Catalan, factorial or a power of two.
Digit curiosities
- Happy number
- No
- Harshad number
- No
- Collatz trajectory
- 27 steps to 1
Summing the squares of its digits falls into the 4 → 16 → 37 → … → 4 cycle.
Not divisible by its digit sum 11.
Peaks at 196 along the way.
Written other ways
- Binary
- 1000001
- Octal
- 101
- Hexadecimal
- 41
- Base 36
- 1T
- Roman numerals
- LXV
- In words
- sixty-five
- Scientific notation
- 6.5 × 10^1
Is 65 a prime number?
Composite — it factors as 5 × 13.
Nearby numbers
Other numeral systems
Beyond the bases and Roman numerals above, these notations write 65 their own way.
- Greek (alphabetic)
- ΞΕʹ
- Babylonian cuneiform
- 𒐕𒐙
- Tamil
- ௬௰௫
References
Further reading: Wikipedia · Wikidata
Notations, naming and the links above come from Wikidata, whose structured data is dedicated to the public domain under CC0-1.0. Retrieved 2026-10-07.