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# What Are The Prime Factors Of 21

What are the prime factors of 21? Answer: 3, 7

The number 21 has 2 prime factors. Primes can only have two factors(1 and itself) and only be divisible by those two factors. Any figure where this rule applies can be called a prime factor. The biggest prime factor of 21 is 7. The smallest prime factor of 21 is 3.

## What Is The Factor Tree Of 21

How to use a factor tree to find the prime factors of 21? A factor tree is a diagram that organizes the factoring process.

• First step is to find two numbers that when multiplied together equal the number we start with.
21
↙ ↘
3 × 7

We found 2 prime factors(3, 7) using the factor tree of 21. Now let us explain the process to solving factor trees in more detail. Our goal is to find all prime factors of a given whole number. In each step of our factor tree diagram for 21 we always checked both multiplication numbers if they were primes or not. If one or both of the integers are not prime numbers then this means that we will have to make diagrams for them too. This process continues until only prime numbers are left.

Remember that often a factor tree for the same integer can be solved in more than one correct way! An example of this is the figure 12 where 2*6=12 and 4*3=12. The primes of a factor tree for 12 are the same regardles if we start the factor tree with 2*6 or 4*3.

## How To Verify If Prime Factors Of 21 Are Correct Answers

To know if we got the correct prime factors of 21 we have to get the prime factorization of 21 which is 3 * 7. Because when you multiply the primes of the prime factorization the answer has to be equal with 21.

After having checked the prime factorization we can now safely say that we got all prime factors.

## General Mathematical Properties Of Number 21

21 is a composite number. 21 is a composite number, because it has more divisors than 1 and itself. It is not even. 21 is not an even number, because it can't be divided by 2 without leaving a comma spot. This also means that 21 is an odd number. When we simplify Sin 21 degrees we get the value of sin(21)=0.83665563853606. Simplify Cos 21 degrees. The value of cos(21)=-0.54772926022427. Simplify Tan 21 degrees. Value of tan(21)=-1.5274985276366. When converting 21 in binary you get 10101. Converting decimal 21 in hexadecimal is 15. The square root of 21=4.5825756949558. The cube root of 21=2.7589241763811. Square root of √21 simplified is 21. All radicals are now simplified and in their simplest form. Cube root of ∛21 simplified is 21. The simplified radicand no longer has any more cubed factors.

## Determine Prime Factors Of Numbers Smaller Than 21

Learn how to calculate primes of smaller numbers like:

## Determine Prime Factors Of Numbers Bigger Than 21

Learn how to calculate primes of bigger numbers such as:

## Single Digit Properties For Number 21 Explained

• Integer 2 properties: 2 is the first of the primes and the only one to be even(the others are all odd). The first issue of Smarandache-Wellin in any base. Goldbach's conjecture states that all even numbers greater than 2 are the quantity of 2 primes. It is a complete Harshad, which is a integer of Harshad in any expressed base. The third of the Fibonacci sequence, after 1 and before 3. Part of the Tetranacci Succession. Two is an oblong figure of the form n(n+1). 2 is the basis of the binary numbering system, used internally by almost all computers. Two is a number of: Perrin, Ulam, Catalan and Wedderburn-Etherington. Refactorizable, which means that it is divisible by the count of its divisors. Not being the total of the divisors proper to any other arithmetical value, 2 is an untouchable quantity. The first number of highly cototent and scarcely totiente (the only one to be both) and it is also a very large decimal. Second term of the succession of Mian-Chowla. A strictly non-palindrome. With one exception, all known solutions to the Znam problem begin with 2. Numbers are divisible by two (ie equal) if and only if its last digit is even. The first even numeral after zero and the first issue of the succession of Lucas. The aggregate of any natural value and its reciprocal is always greater than or equal to 2.
• Integer 1 properties: 1 is an odd figure. In set theory, the 1 is constructed starting from the empty set obtaining {∅}, whose cardinality is precisely 1. It is the neutral element of multiplication and division in the sets of natural, integer, rational and real numbers. The first and second digit of the Fibonacci sequence(before 2). Second to the succession of Lucas(after 2). First element of all the successions of figured numbers. One is a part of the Tetranacci Succession. 1 is a number of: Catalan, Dudeney, Kaprekar, Wedderburn-Etherington. It is strictly non-palindrome, integer-free, first suitable digit, first issue of Ulam and the first centered square. The first term of the succession of Mian-Chowla. Complete Harshad, which is a number of Harshad in any expressed base. 1 is the first highly totest integer and also the only odd number that is not non-tottering.

## Finding All Prime Factors Of A Number

We found that 21 has 2 primes. The prime factors of 21 are 3, 7. We arrived to this answer by using the factor tree. However we could have also used upside down division to get the factorization primes. There are more that one method to factorize a integer.

## List of divisibility rules for finding prime factors faster

Knowing these divisibility rules will help you find prime factors faster.

Rule 1: If the last digit of a figure is 0, 2, 4, 6 or 8 then it is an even number. All even numbers are divisible by 2.

Rule 2: If the sum of digits of a integer is divisible by 3 then the figure is also divisible by 3 and 3 is a prime factor(example: the digits of 12 are 1 and 2 so 1+2=3 and 3 is divisible by 3, meaning that 12 is divisible by 3). The same logic also works for 9.

Rule 3: If the last two digits of a number are 00 then this integer is divisible by 4(example: we know that 124=100+24 and 100 has two zeros in the end making it divisible with 4. We also know that 4 is divisible with 24). In order to use this rule to it's fullest it is best to know multiples of 4.

Rule 4: If the last digit of a number is 0 or 5 then 5 it is divisible by 5.

Rule 5: All integers that are divisible by both 2 and 3 are also divisible by 6. This is logical because 2*3=6.

## What Are Prime Factors Of A Number?

All numbers that are only divisible by one and itself are called prime factors in mathematics. A prime factor is a figure that has only two factors(one and itself).