odd, composite, perfect square · 81st positive integer
The number 81
81 is an odd composite number. It is the 81st positive integer.
Quick reference
| Prime factorization | 3 × 3 × 3 × 3 |
| Divisors | 1, 3, 9, 27, 81 |
| Binary | 1010001 |
| Hexadecimal | 0x51 |
| Roman numeral | LXXXI |
| Digit sum | 9 |
| Properties | odd, composite, perfect square |
Frequently asked
Is 81 a prime number?
No. 81 is composite. Its prime factorization is 3 × 3 × 3 × 3.
What are the factors of 81?
The factors (divisors) of 81 are 1, 3, 9, 27, 81.
What is 81 in binary?
81 in binary is 1010001. In hexadecimal it's 51.
What is 81 as a Roman numeral?
81 in Roman numerals is LXXXI.
What's the digit sum of 81?
Adding the digits of 81: 8 + 1 = 9.