# 821

## 821 is a prime number. Like all primes greater than two, it is odd and has no factors apart from itself and one.

What does the number 821 look like?

As a prime, it is not composed of any other numbers and has no internal structure.

821 is a prime number. Like all primes (except two), it is an odd number.

## Prime factorization of 821:

### 821

See below for interesting mathematical facts about the number 821 from the Numbermatics database.

### Names of 821

• Cardinal: 821 can be written as Eight hundred twenty-one.

### Scientific notation

• Scientific notation: 8.21 × 102

### Factors of 821

• Number of distinct prime factors ω(n): 1
• Total number of prime factors Ω(n): 1
• Sum of prime factors: 821

### Divisors of 821

• Number of divisors d(n): 2
• Complete list of divisors:
• Sum of all divisors σ(n): 822
• Sum of proper divisors (its aliquot sum) s(n): 1
• 821 is a deficient number, because the sum of its proper divisors (1) is less than itself. Its deficiency is 820

### Bases of 821

• Binary: 11001101012
• Base-36: MT

### Squares and roots of 821

• 821 squared (8212) is 674041
• 821 cubed (8213) is 553387661
• The square root of 821 is 28.6530975637
• The cube root of 821 is 9.3637049155

### Scales and comparisons

How big is 821?
• 821 seconds is equal to 13 minutes, 41 seconds.
• To count from 1 to 821 would take you about six minutes.

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. (We do not count involuntary pauses, bathroom breaks or the necessity of sleep in our calculation!)

• A cube with a volume of 821 cubic inches would be around 0.8 feet tall.

### Recreational maths with 821

• 821 backwards is 128
• 821 is a twin prime! Its twin is 823
• The number of decimal digits it has is: 3
• The sum of 821's digits is 11
• More coming soon!