81
Everything about the number 81 — its names, how to write it in other bases and numeral systems, and what makes it interesting mathematically.
Advertisement
Names of 81
| Nominal | 81 |
| Cardinal | eighty-one |
| Ordinal | 81st |
| This number as US currency | eighty-one dollars |
Properties (and some facts) of 81
| Is 81 an odd number? | 81 is an odd number |
| Is 81 an even number? | 81 is not an even number |
| Is 81 a palindrome? | 81 is not a palindrome |
| Is 81 a triangle number? | 81 is not a triangle number |
Advertisement
81 in other bases
| Base 2 (Binary) | 1010001 |
| Base 3 (Ternary) | 10000 |
| Base 4 (Quaternary) | 1101 |
| Base 5 (Quinary) | 311 |
| Base 6 (Senary) | 213 |
| Base 8 (Octal) | 121 |
| Base 12 (Duodecimal) | 69 |
| Base 16 (Hexadecimal) | 51 |
| Base 20 (Vigesimal) | 41 |
Primes and factors tests for 81
| Is 81 a prime number? | 81 is not a prime number |
| Is 81 a perfect number? | 81 is not a perfect number |
| Is 81 a Mersenne prime? | 81 is not a Mersenne prime |
| Is 81 a Fermat prime? | 81 is not a Fermat prime |
| Is 81 a Fibonacci prime? | 81 is not a Fibonacci prime |
| Is 81 a partition prime? | 81 is not a partition prime |
| Is 81 a Pell prime? | 81 is not a Pell prime |
| Prime Factors | Prime factors of 81 |
81 in other numeral systems
| 81 in Roman numerals | LXXXI |
| 81 in Chinese numerals | 捌拾壹 |
| 81 in Babylonian numerals |   |
| 81 in Egyptian numerals | 𓎍𓏺 |
Roots and squares for 81
| Is 81 a square number? | 81 is a square number |
| Is 81 a cube number? | 81 is not a cube number |
| Square root of 81 | 9 |
| Cube root of 81 | 4.3267487109222 |
Recreational math for 81
| Number 81 reversed | 18 |
| Sum of the digits | 9 |
| Number of digits | 2 |
Arithmetic tables for 81
Other pages about 81
Advertisement