Number analysis
25
25 is a composite odd number that factors as 5^2.
25 is a composite odd number that factors as 5^2.
The number itself
- Value
- 25
- Digits
- 2
- Digit sum
- 7
- Reversed
- 52
- Palindrome
- No
2 + 5
Digit sum repeated until one digit remains; equals n mod 9 (with 9 for multiples of 9).
Reverses to 52.
Parity and primality
- Parity
- Odd
- Prime
- No
- Squarefree
- No
- Semiprime
- Yes
- Prime power
- 5^2
- Powerful
- Yes
- Möbius μ(n)
- 0
- Nearest primes
- 23 ← → 29
Leaves remainder 1 on division by 2.
Composite — it factors as 5^2.
1 distinct prime factor, 2 with multiplicity.
At least one prime appears squared.
A product of exactly two primes, counted with multiplicity.
A single prime raised to a power.
Every prime factor appears at least squared.
Zero, because a squared prime divides n.
A gap of 6 between them.
Divisors
- Aliquot sum
- 6
- Classification
- Deficient
1, 5, 25
The proper divisors — everything except n itself.
Its proper divisors fall short by 19.
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
0² + 5² = 25 · 3² + 4² = 25
Legendre's three-square theorem allows it.
Lagrange's four-square theorem: every non-negative integer is, without exception.
Shapes and sequences
- Square number
- Yes — the 5th
Digit curiosities
- Happy number
- No
- Harshad number
- No
- Automorphic
- Yes
- Collatz trajectory
- 23 steps to 1
Summing the squares of its digits falls into the 4 → 16 → 37 → … → 4 cycle.
Not divisible by its digit sum 7.
Its square 625 ends in 25.
Peaks at 88 along the way.
Written other ways
- Binary
- 11001
- Octal
- 31
- Hexadecimal
- 19
- Base 36
- P
- Roman numerals
- XXV
- In words
- twenty-five
- Scientific notation
- 2.5 × 10^1
Is 25 a prime number?
Composite — it factors as 5^2.
Nearby numbers
Other numeral systems
Beyond the bases and Roman numerals above, these notations write 25 their own way.
- Greek (alphabetic)
- ΚΕʹ
- Babylonian cuneiform
- 𒎙𒐙
- Tamil
- ௨௰௫
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.