# 81

## 81 is an odd composite number. It is composed of a single prime number multiplied by itself three times.

81 is an odd composite number. It is composed of one distinct prime number multiplied by itself three times. It has a total of five divisors.

## Prime factorization of 81:

### 34

(3 × 3 × 3 × 3)

See below for interesting mathematical facts about the number 81 from the Numbermatics database.

### Names of 81

• Cardinal: 81 can be written as Eighty-one.

### Scientific notation

• Scientific notation: 8.1 × 101

### Factors of 81

• Number of distinct prime factors ω(n): 1
• Total number of prime factors Ω(n): 4
• Sum of prime factors: 3

### Divisors of 81

• Number of divisors d(n): 5
• Complete list of divisors:
• Sum of all divisors σ(n): 121
• Sum of proper divisors (its aliquot sum) s(n): 40
• 81 is a deficient number, because the sum of its proper divisors (40) is less than itself. Its deficiency is 41

### Bases of 81

• Binary: 1010001 2

### Squares and roots of 81

• 81 squared (812) is 6561
• 81 cubed (813) is 531441
• 81 is a perfect square number. Its square root is 9
• The cube root of 81 is 4.3267487109

### Scales and comparisons

How big is 81?
• 81 seconds is equal to 1 minute, 21 seconds.
• To count from 1 to 81 would take you about forty seconds.

This is a very rough estimate, based on a speaking rate of half a second every third order of magnitude. If you speak quickly, you could probably say any randomly-chosen number between one and a thousand in around half a second. Very big numbers obviously take longer to say, so we add half a second for every extra x1000.

Note: we do not count involuntary pauses, bathroom breaks or the necessity of sleep in our calculation!

• A cube with a volume of 81 cubic inches would be around 0.4 feet tall.

### Recreational maths with 81

• 81 backwards is 18
• 81 is a Harshad number.
• The number of decimal digits it has is: 2
• The sum of 81's digits is 9
• More coming soon!

The information we have on file for 81 includes mathematical data and numerical statistics calculated using standard algorithms and methods. We are adding more all the time. If there are any features you would like to see, please contact us. Information provided for educational use, intellectual curiosity and fun!

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