Number
18
18 is a composite number, even, a calendar year.
Properties
- Parity
- Even
- Digit count
- 2
- Digit sum
- 9
- Digital root
- 9
- Palindrome
- No
- Divisor count
- 6
- σ(n) — sum of divisors
- 39
Primality
Prime factorization: 2 × 3 2
Divisors & multiples
Aliquot sum (sum of proper divisors):
21
Representations
- In words
- eighteen
- Ordinal
- 18th
- Roman numeral
- XVIII
- Binary
- 10010
- Octal
- 22
- Hexadecimal
- 12
Also seen as
Goldbach decomposition
Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 18, here are decompositions:
- 5 + 13 = 18
- 7 + 11 = 18
ASCII character
As an ASCII codepoint, 18 is control character (0x12). ASCII control character.
Hex color
#000012
RGB(0, 0, 18)
IPv4 address
As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.18.