Number
81
81 is a composite number, odd, a calendar year.
Properties
- Parity
- Odd
- Digit count
- 2
- Digit sum
- 9
- Digital root
- 9
- Palindrome
- No
- Divisor count
- 5
- σ(n) — sum of divisors
- 121
Primality
Prime factorization: 3 4
Divisors & multiples
Aliquot sum (sum of proper divisors):
40
Representations
- In words
- eighty-one
- Ordinal
- 81st
- Roman numeral
- LXXXI
- Binary
- 1010001
- Octal
- 121
- Hexadecimal
- 51
Also seen as
ASCII character
As an ASCII codepoint, 81 is Q. Printable ASCII character Q.
Hex color
#000051
RGB(0, 0, 81)
IPv4 address
As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.81.