Page 4 - Arithmetic

REMEMBER:
2 is the only even prime number
0 and 1 are not prime numbers
First 15 prime numbers are: 2,3,5,7,11,13,17,19, 23,29,31, 37, 41, 43, and 47
Prime numbers greater than 100
Step 1: Find a whole number ‘y’ which is greater than the square root of the number ‘x’. Step 2: y > √𝑥
You can easily find the prime numbers less than 100. But, how do you know if a number greater
than 100 is prime or not?
Let ‘x’ be the number greater than 100. If you want to know whether the number is a prime
number or not, perform the following steps.
Step 3: Test whether the number ‘x’ is divisible by any prime number less than ‘y’. If it’s divisible
then the number is not a prime number, else it’s prime.
Worked Example 1
Is 421 a prime number?
Solution:
14 > √421
Prime numbers less than 14 are 2, 3, 5, 7, 11, and 13
421 is not divisible by any of the numbers.
So, 421 is a prime number.
Composite numbers
All the natural numbers that are divisible by more than 1 and itself are called composite numbers.
For example,
REMEMBER:
1 is not a composite number
10 is a composite number because it’s divisible by 2, 5, 10, and 1.
Odd numbers
Any integer which leaves a remainder of 1, 3, 5, 7, and 9 on dividing by 2 is called an odd number.
For example,
Page 3 of 55
Arithmetic Concept