How do we find whether a number is prime or not? Let us check out the various methods to learn when we have to check if a number is a prime number.

The counting divisors method for 72 would simply be
Divisors of 72= 1,2,3,4,6,8,9,12,18,24,36,72
Number of divisors= 12
The number 72 can be considered composite.
In the divisibility method, the prime number only has 2 divisors, which are 1 and itself.
Divisors of 72=1,2,3,4,6,8,9,12,18,24,36,72
As 72 has factors more than 2 then it is not a prime number.


The list of prime numbers under 100 are;
2,3,5,7,11,13,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97.
72 is not present in the list, it is not a prime number.
This method is only used for a non-prime number/composite number. Since 72 is a composite number, prime factorization for 72 is :
Factors of 72 = 2×2×2×3×3

It is highly likely we commit some mistakes due to confusion or unclear understanding. Let us look at possible mistakes we may make and try to avoid them.
Thinking that all odd numbers are prime
not all odd numbers are prime numbers. A composite number can still be an odd number.
Skipping out the divisors
without checking all the divisors of a number of students incorrectly conclude a number is prime or composite. Avoid doing this.
Thinking prime numbers should fall in a range only
Prime numbers do not have range as long as the criteria of having 2 divisors is fulfilled the prime number can be any number.
yes. 4 and 6 are a relatively prime number pair.
GCF(44,66) = 11
to find the GCF we list the factors of 44 and 66 and find the highest value of them all. In this case the highest value of the numbers that is common is 11.
to find the GCF we first list out the factors of the numbers and find the highest factor that is common for both the numbers.
The GCF of 40 and 100 is 20.
When we find the GCF of any numbers, we list the factors of the numbers and find the highest common factor between the numbers,
GCF(52,65) = 13.
to find the GCF of any numbers, →list the factors and find the highest common factor.
The GCF of 11 and 13 is 1.
Hiralee Lalitkumar Makwana has almost two years of teaching experience. She is a number ninja as she loves numbers. Her interest in numbers can be seen in the way she cracks math puzzles and hidden patterns.
: She loves to read number jokes and games.
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