Number analysis
2
The only even prime, which is why it is sometimes called the oddest prime.
The only even prime, which is why it is sometimes called the oddest prime.
The number itself
- Value
- 2
- Digits
- 1
- Digit sum
- 2
- Reversed
- 2
- Palindrome
- Yes
2
Digit sum repeated until one digit remains; equals n mod 9 (with 9 for multiples of 9).
Reads the same in both directions.
Parity and primality
- Parity
- Even
- Prime
- Yes
- Squarefree
- Yes
- Möbius μ(n)
- -1
- Sophie Germain prime
- Yes — 2n+1 = 5 is also prime
- Nearest primes
- — ← → 3
Divisible by 2.
Divisible only by 1 and itself.
1 distinct prime factor, 1 with multiplicity.
No prime divides it twice.
(−1) to the power of 1 distinct prime factors.
Divisors
- Aliquot sum
- 1
- Classification
- Deficient
1, 2
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
- 1³ + 1³
1² + 1² = 2
Legendre's three-square theorem allows it.
Lagrange's four-square theorem: every non-negative integer is, without exception.
Shapes and sequences
- Fibonacci number
- Yes — index 3
- Lucas number
- Yes — index 0
- Catalan number
- Yes — index 2
- Factorial
- Yes — 2!
- Power of two
- Yes — 2^1
Digit curiosities
- Happy number
- No
- Armstrong number
- Yes, trivially
- Harshad number
- Yes
- Collatz trajectory
- 1 step to 1
Summing the squares of its digits falls into the 4 → 16 → 37 → … → 4 cycle.
Every single-digit number equals itself raised to the first power, so all ten qualify trivially.
Divisible by its digit sum 2 — 2 ÷ 2 = 1.
Peaks at 2 along the way.
Written other ways
- Binary
- 10
- Octal
- 2
- Base 36
- 2
- In words
- two
- Scientific notation
- 2 × 10^0
Is 2 a prime number?
Yes. 2 has no divisors other than 1 and itself.
Nearby numbers
Other numeral systems
Beyond the bases and Roman numerals above, these notations write 2 their own way.
- Greek (alphabetic)
- Βʹ
- Babylonian cuneiform
- 𒐖
- Tamil
- ௨
References
Further reading: Wikipedia · MathWorld · 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.