### The Number

# 21

## Twenty-One

## Nearby Numbers

*Positive, nonzero integers within three units*

## Scientific Notation

*Scientific notation expresses a quantity as the product of its significand with 10 raised to an integer exponent.*

`2.1e1`

## Reciprocal

*A number multiplied with its reciprocal is one.*

`0.047619047619047616`

The reciprocal of 21.

## Palindrome?

*A numerical palindrome has the same value when all of its digits are reversed.*

The number 21 is not a palindrome.

## Not A Prime Number

*A prime number is a positive integer that is divisible only by itself and one.*

Twenty-one is a composite number with 4 total factors (including 1 and itself). See primes in Base 10 Decimal

## A Composite

*Composites have more than just these two factors.*

Twenty-one is a composite number with 4 total factors (including 1 and itself).

## Prime Factors

*The prime factors of a positive integer are the integers that divide it exactly and are also prime.*

The number twenty-one has the following 2 prime factors:

## Prime Factorization

*The prime factorization of a positive integer is the unique list of prime factors together with their multiplicities*

###
```
31
·
71
= 21
```

## Base Conversions

*The number twenty-one in 35 different bases*