Number 81 - properties and curiosities

81 (number)

81

Number 81 properties

  • Perfect square
  • Harshad
  • 81 is an odd number.
  • 81 is a perfect square (9 × 9).
  • 81 is a Harshad number, which means it is divisible by the sum of its digits (81 = 9, and 81 is divisible by 9).

Prime factorization

Prime factorization of 81: 3^4.

Divisors

Divisor count: 5

1, 3, 9, 27, 81

Factors of 81 are: 1, 3, 9, 27, 81.

Representations

In octal, 81 is represented as 121.

In binary, 81 is represented as 1010001.

In hex, 81 is represented as 51.

Roman numeral: LXXXI

Curiosities

  • 81 is a perfect square, so it forms a square grid with equal side lengths.
  • 81 is divisible by the sum of its digits.

Quick answers

Is 81 prime?
No, 81 is not prime.

What are the factors of 81?
1, 3, 9, 27, 81

What is 81 in binary?
1010001