In this post, we will learn how to print prime numbers in python from 1 to 100, 1 to n, and in a given interval but before we jump into a program let’s understand what is a prime number?

## What is a prime number?

A natural number that is only divisible by 1 and itself is called a prime number.

For example: 2,3,5,7,11,13,17,19….

## Algorithm to Print Prime Numbers from 1 to 100

Step-1: iterate a for loop in range 2 to100 –> `for i in range(2,101)`

Step-2: inside the first loop create another for loop in the range 2 to 100 –> `for j in range(2,101)`

Step-3: check if `i%j == 0` then break a loop (Because a number is not prime)

Step-4: step-3 implies that if a number `i` is not divisible by` j` then the program never enters in if-block, this means at the end of the second for-loop `i == j`

Step-5: if `i == j` then print `i` ( Because `i` is your prime number)

Now we understand what is prime number and how to implement a prime number program in python so now it’s time to do it practically.

## 1. Write a python program to print prime numbers from 1 to 100 using a for loop

Few concepts you know before writing this program such as

1. For loop
2. nested for loop
3. if-else

Source code:

``````for i in range(2,101):   # The range() function does not include the last number (the ending number). Only numbers from 2 to 100 are counted.
for j in range(2,101):
if i%j == 0:
break
if i == j:
print(i,end=",")``````

Output:

``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,``

## 2. Write a python program to print prime numbers from 1 to 100 using a while loop

In the case of a while loop Above algorithm is used only syntax is changed.

Few concepts you know before writing this program such as

1. while loop
2. nested while loop
3. if-else

Source code:

``````i = 2

while i <= 100:
j = 2
while j < 100:
if i%j == 0:
break
j += 1
if i == j:
print(i,end=',')
i += 1``````

Output:

``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,``

## 3. Write a python program to print prime numbers from 1 to N using a for loop

NOTE: In this program, we will change only the user input `num` with the static value `101` of the above program.

Few concepts you know before writing this program such as

1. how to take user input
2. for loop
3. nested for loop
4. if-else

Source code:

``````num = int(input("Enter a number: "))

for i in range(2,num+1):
for j in range(2,num+1):
if i%j == 0:
break
if i == j:
print(i,end=',')``````

Output:

``````Enter a number: 50
2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,``````

## 4. Write a python program to print prime numbers from 1 to N using a while loop

NOTE: In this program, we will change only the user input `num` with the static value `100` of the above program.

Few concepts you know before writing this program such as

1. how to take user input
2. while loop
3. nested while loop
4. if-else

Source code:

``````num = int(input("Enter a number: "))
i = 2

while i <= num:
j = 2
while j < num:
if i%j == 0:
break
j += 1
if i == j:
print(i,end=',')
i += 1``````

Output:

``````Enter a number: 70
2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,``````

## 5. write a python program to print prime numbers in a given range using a for loop

NOTE: In this program, we will change only the upper limit and lower limit of the `range()` function with user input.

Source code:

``````num1 = int(input("Enter a first number: ")) #lower limit
num2 = int(input("Enter a second number: ")) #upper limit

if num1<num2:
for i in range(num1,num2+1):
for j in range(2,num2+1):
if i%j == 0:
break
if i == j:
print(i,end=',')
else:
print('invalid number!')``````

Output:

``````Enter a first number: 4
Enter a second number: 7
5,7,``````

## 6. write a python program to print prime numbers in a given range using a while loop

NOTE: In this program, we will change only the upper limit and lower limit of the while-loop with user input.

``````num1 = int(input("Enter a first number: ")) #lower limit
num2 = int(input("Enter a second number: ")) #upper limit

if num1<num2:
while num1 <= num2:
j = 2
while j < num2:
if num1%j == 0:
break
j += 1
if num1 == j:
print(num1,end=',')
num1 += 1
else:
print('invalid input')``````

Output:

``````Enter a first number: 9
Enter a second number: 19
11,13,17,19,``````

From all the above 6 programs we understand how to print prime number sequences.

This is a bonus for the prime number program.

## Write a python program to create a list of prime numbers from 1 to N

Few concepts you know before writing this program such as

1. python list
2. function in python
3. for loop
4. nested for loop
5. if-else

Source code:

``````def prime_range(num):
prime = []
for i in range(2,num+1):
for j in range(2,num+1):
if i%j == 0:
break
if i == j:
prime.append(i)
return prime

number  = int(input('Enter a number: '))
print(prime_range(number))
print('sum of prime numbers',sum(prime_range(num= number)))
``````

Output:

``````Enter a number: 20
[2, 3, 5, 7, 11, 13, 17, 19]
sum of prime numbers 77``````

Hope this post adds some value to your life – thank you.

Hi, I'm Yagyavendra Tiwari, a computer engineer with a strong passion for programming. I'm excited to share my programming knowledge with everyone here and help educate others in this field.