# Maths: Know The Numbers

1). 0, 1, 2, 3, —-9. are called Digits.

2). 10, 11, 12,—– are called Number.

3). Natural number (N) :- Counting numbers are called natural numbers.

Example:- 1, 2, 3,—etc. are all natural numbers. minimum natural number 1 and maximum natural number ∞

4). Whole numbers (W) :- All counting numbers together with zero from the set of whole numbers
Example:- 0, 1, 2, 3, 4, —— are whole number.

5). Integers (Z) :- All counting numbers, 0 and -ve of counting numbers are called integers.
Example:- -∞———, -3, -2, -1, 0, 1, 2, 3, ——-∞

6). Rational Numbers (Q) :- A Rational Number is a real number that can be written as a simple fraction
Example:- {p/q/p,q∈Z}

7). Irrational Numbers :- An Irrational Number is a real number that cannot be written as a simple fraction.
Example:- √

8). Even numbers :- A number divisible by 2 is called an even number.
Example:- 0, 2, 4, 6, – – – – – – – – –

9). Odd numbers :- A number not divisible by 2 is called an odd number.
Example:- 1, 3, 5, 7, – – – – – –

10). Composite Numbers :- Numbers greater than 1 which are not prime, are called composite numbers.
Example:- 4, 6, 8, 9, 10, – – – -. 6 -> 1,2,3,6.

11). Prime Numbers:- A number greater than 1 having exactly two factors, namely 1 and itself is called a prime number.
Example:- Upto 100 prime numbers are:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 71, 73, 79, 83, 89, 97

12). Co-prime Numbers:- Two natural numbers a and b are said to be co-prime if their HCF is 1.
Example:- (21, 44), (4, 9), (2, 3), – – – – –

13). Twin prime numbers :- A pair of prime numbers (as 3 and 5 or 11 and 13) differing by two are called twin prime number.
Example:- The twin pair primes between 1 and 100 are
(3, 5), (5, 7), (11, 13), (17, 19), (29, 31), (41, 43), (59, 61), (71, 73).

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