# Prime-Composite numbers

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**Prime numbers**: The numbers whose factors are 1 and the number itself is called

__Prime numbers.__

**Example :**2,3,5,7,11,13,…

2 is the smallest even prime number and 3 is the smallest odd prime number.

The prime numbers up to 100 are :

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71,

73, 79, 83, 89, 97

**Composite Number**: The number which has at least one factor other than 1 and the number itself.

**Example**: 4,6,8,9,12,…

**Note : 1 is neither prime nor composite.**

**Co-prime Numbers**: Two numbers that do not have a common factor other than 1.

The first 100 composite numbers are

4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33,

34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58,

60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85,

86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100, 102, 104, 105, 106, 108,

110, 111, 112, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125,

126, 128, 129.

**Example :**35 and 39

35 = 7 x 5 x 1

39 = 3 x 13 x 1

Both 35 and 39 are composite numbers,the only factor common between them is 1.

∴ 35 and 39 are co-prime numbers.

**Some more examples are**: 1) 2,3 ; 2) 3,4 3) 5,6 4) 8,13, and so on.

**Twin Primes**: Two prime number are known as twin primes of there is only one composite number between them.

The twin primes between 1 to 100 are

3-5, 5-7, 11-13, 17-19, 29-31, 41-43, 59-61, 71-73

**Factors and Multiples**

• Prime-Composite numbers

• Divisibility rules

• Prime Factorization

• H.C.F or G.C.F

• L.C.M

• Application on LCM

Number System

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