Number analysis
45
45 is a composite odd number that factors as 3^2 × 5.
45 is a composite odd number that factors as 3^2 × 5.
The number itself
- Value
- 45
- Digits
- 2
- Digit sum
- 9
- Reversed
- 54
- Palindrome
- No
4 + 5
Digit sum repeated until one digit remains; equals n mod 9 (with 9 for multiples of 9).
Reverses to 54.
Parity and primality
- Parity
- Odd
- Prime
- No
- Prime factorisation
- 3^2 × 5
- Squarefree
- No
- Möbius μ(n)
- 0
- Nearest primes
- 43 ← → 47
Leaves remainder 1 on division by 2.
Composite — it factors as 3^2 × 5.
2 distinct prime factors, 3 with multiplicity.
At least one prime appears squared.
Zero, because a squared prime divides n.
A gap of 4 between them.
Divisors
- Aliquot sum
- 33
- Classification
- Deficient
1, 3, 5, 9, 15, 45
The proper divisors — everything except n itself.
Its proper divisors fall short by 12.
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
3² + 6² = 45
Legendre's three-square theorem allows it.
Lagrange's four-square theorem: every non-negative integer is, without exception.
Shapes and sequences
- Triangular number
- Yes — the 9th
- Hexagonal number
- Yes — the 5th
Digit curiosities
- Happy number
- No
- Harshad number
- Yes
- Kaprekar number
- Yes
- Collatz trajectory
- 16 steps to 1
Summing the squares of its digits falls into the 4 → 16 → 37 → … → 4 cycle.
Divisible by its digit sum 9 — 45 ÷ 9 = 5.
Peaks at 136 along the way.
Written other ways
- Binary
- 101101
- Octal
- 55
- Hexadecimal
- 2D
- Base 36
- 19
- Roman numerals
- XLV
- In words
- forty-five
- Scientific notation
- 4.5 × 10^1
Is 45 a prime number?
Composite — it factors as 3^2 × 5.
Nearby numbers
Other numeral systems
Beyond the bases and Roman numerals above, these notations write 45 their own way.
- Greek (alphabetic)
- ΜΕʹ
- Babylonian cuneiform
- 𒐏𒐙
- Tamil
- ௪௰௫
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.