Even Numbers :

Any Number that can be divided exactly by 2

The digit in once place is 0, 2, 4, 6 or 8

Ex: 2,6,12,18,20

Odd Numbers :

Any integer that cannot be divided exactly by 2

The digit in once place is 1, 3, 5, 7 or 9

Ex : 7,9,15,19

Factor

A number which divides the other number exactly is called a factor of that number

• 1 is a factor of every number and is the smallest of all factors.
• Every number is a factor of itself and is the greatest of its factors.
• Every factor is less than or equal to the given number.
• Number of factors of a given number is countable

Prime numbers:

These numbers whose only factors are 1 and the number itself

are called prime numbers.

Ex : 3,5,7,11,13,17

Composite numbers.

Numbers having more than two factors are called composite numbers.

Ex : 4,6,10,12

• The number 1 has only one factor (i.e. itself) so, 1 is neither prime nor composite.

 

 

Co-primes or relatively prime

The numbers which have only 1 as the common factor are called co-primes or relatively prime

Ex : (5,8)  (10,11)

• We can say that "Only two primes are co-primes but all the co-primes need not be primes."

Twin primes :

Twin primes are prime numbers that differ from each other by two

Ex : (3,5) (5,7) (11,13)

Highest Common Factor (HCF) :

The Highest Common Factor (HCF) of two or more given numbers is the highest (or greatest) of their common factors. It is also called as Greatest Common Divisor (GCD)

Least common Multiple (LCM) :

The least common multiple of two or more given numbers is the lowest (or smallest or least) of their common multiples

• Product of LCM and HCF of the two numbers = Product of the two numbers