# Is 21 a Prime Number?

Is 21 a prime number? * "No, 21 is not a prime number."* A number can be classified as prime or composite depending on the factors it contains; it could either have only 2 factors or more than 2 factors. Numbers like 631 with only 2 factors, i.e. 1 and 631 are called prime numbers. However, numbers like 340 with more than 2 factors are called composite numbers. Let us find out how and why is 21 a prime number or a composite number?

**Is 21 a prime number? -**No**Is 21 a composite number? -**Yes**Prime Factors of 21 -**3, 7**Is 21 a perfect square? -**No**Factors of 21 -**1, 3, 7, 21

## Is 21 a Prime Number?

No, 21 is not a prime number. The number 21 is divisible by 1, 3, 7, 21. For a number to be classified as a prime number, it should have exactly two factors. Since 21 has more than two factors, i.e. 1, 3, 7, 21, it is not a prime number.

## Why is 21 not a Prime Number?

To understand whether 21 is prime or composite, it is important to find its factors.

**Factors of 21:** 1, 3, 7, 21

Since 21 has more than 2 factors, we can say that 21 is not a prime number.

## Is 21 a Composite Number?

Yes, since 21 has more than two factors i.e. 1, 3, 7, 21. In other words, 21 is a composite number because 21 has more than 2 factors.

**Problem Statements: **

Is 21 a Prime Number? | No |

Is 21 a Composite Number? | Yes |

Is 21 a Perfect Square? | No |

Is 21 an Odd Number? | Yes |

Multiples of 21 | 21, 42, 63, 84, 105, 126, 147, 168, 189, 210 |

Cube Root of 21 | 2.758921 |

Is 21 an Even Number? | No |

Is 21 a Perfect Cube? | No |

Square Root of 21 | 4.582576 |

Square of 21 | 441 |

**Fun Facts: **

- Numbers X and Y are said to be coprime if they have only one common factor that is 1.
- All primes except 2 are odd.
- 23 is the smallest prime number having consecutive digits.

**☛ Also Check: **

- Is 100 a Prime Number? - No
- Is 289 a Prime Number? - No
- Is 127 a Prime Number? - Yes
- Is 36 a Prime Number? - No
- Is 71 a Prime Number? - Yes
- Is 571 a Prime Number? - Yes
- Is 96 a Prime Number? - No
- Is 180 a Prime Number? - No

visual curriculum