Number analysis
128
128 is a composite even number that factors as 2^7.
128 is a composite even number that factors as 2^7.
The number itself
- Value
- 128
- Digits
- 3
- Digit sum
- 11
- Reversed
- 821
- Palindrome
- No
1 + 2 + 8
Digit sum repeated until one digit remains; equals n mod 9 (with 9 for multiples of 9).
Reverses to 821.
Parity and primality
- Parity
- Even
- Prime
- No
- Squarefree
- No
- Prime power
- 2^7
- Powerful
- Yes
- Möbius μ(n)
- 0
- Nearest primes
- 127 ← → 131
Divisible by 2.
Composite — it factors as 2^7.
1 distinct prime factor, 7 with multiplicity.
At least one prime appears squared.
A single prime raised to a power.
Every prime factor appears at least squared.
Zero, because a squared prime divides n.
A gap of 4 between them.
Divisors
- Aliquot sum
- 127
- Classification
- Deficient
1, 2, 4, 8, 16, 32, 64, 128
The proper divisors — everything except n itself.
Its proper divisors fall short by 1.
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
- 4³ + 4³
- Goldbach pair
- 19 + 109
8² + 8² = 128
Legendre's three-square theorem allows it.
Lagrange's four-square theorem: every non-negative integer is, without exception.
The smallest pair of primes summing to n. Goldbach’s conjecture says one always exists; it remains unproven.
Shapes and sequences
- Power of two
- Yes — 2^7
Digit curiosities
- Happy number
- No
- Harshad number
- No
- Collatz trajectory
- 7 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 128 along the way.
Written other ways
- Binary
- 10000000
- Octal
- 200
- Hexadecimal
- 80
- Base 36
- 3K
- Roman numerals
- CXXVIII
- In words
- one hundred and twenty-eight
- Scientific notation
- 1.28 × 10^2
Is 128 a prime number?
Composite — it factors as 2^7.
Nearby numbers
Other numeral systems
Beyond the bases and Roman numerals above, these notations write 128 their own way.
- Morse code
- · − − − − · · − − − − − − · ·
- Devanagari
- १२८
- Tamil
- ௱௨௰௮
- Thai
- ๑๒๘
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.