What is Prime Number?
Any Natural number greater than 1, which is divisible by 1 and only by itself is called Prime Number.
2, 3, 5, 7, 11 etc.
2 is the smallest Prime Number.
Arrangement of prime numbers
Prime numbers can be arranged in a line form like shown as below in the diagram.
What is composite number?
Any Natural number, which is greater than 1 and is not a Prime Number is called a Composite Number.
4, 6, 8, 9, 10 etc.
1 is neither a Prime Number nor Composite Number.
Every number in maths can either be a prime or a composite number except 0 and 1 because 0 and 1 are neither a prime number nor a composite number.
Arrangement of composite numbers
Composite numbers can be arranged in a rectangular or square form like shown as below in the diagram.
What are coprimes?
Two numbers are called to be coprime or co-prime if they have only 1 as a common factor.
In other way, we can say if greatest common divisor of two numbers is 1, then the two numbers are coprimes.
(2,3), (14,15), (8,13) etc.
What is twin prime?
Two numbers are called Twin Prime if they differ by 2 only or we can say that there is only one composite number between them. One prime number can be 2 more or 2 less than another prime number.
(3,5), (29,31), (71,73) etc.
What are prime triplets?
A set of three consecutive Prime Numbers if the smallest and the largest differ by 6 and must be in the form of (p, p + 2, p + 6) is called a Prime Triplet.
(5,7,11)
Why?
Because, 5, 7 and 11 is in the form of p, p + 2, p + 6
where p = 5
p + 2 = 5 + 2 = 7
and p + 6 = 5 + 6 = 11