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?

**Table of Contents**hide

## 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

then break a loop (Because a number is not prime)**i%j == 0**

**Step-4:** step-3 implies that if a number

is not divisible by**i**` `

then the program never enters in if-block, this means at the end of the second for-loop **j****i == j**

**Step-5: **if

then print **i == j**

( Because **i**

is your prime number)**i**

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

**Source code:**

```
# range function is not count last number (Ending number)
# only 1 to 100 is counted
for i in range(2,101):
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

- while loop
- nested while loop
- 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

- how to take user input
- for loop
- nested for loop
- 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

- how to take user input
- while loop
- nested while loop
- 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

- python list
- function in python
- for loop
- nested for loop
- 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.

## 4 Comments

Its amazing,

Hello.

In second code why should be i==j?

Hello.

In second code why should be i==j?

I mean second code in part 5.

In the given code, the condition “i == j” is used to determine if the variable ‘i’ is a prime number. It checks if the inner loop, which runs from 2 to ‘i’, has reached the value of ‘i’ without finding any divisor other than 1 and ‘i’ itself. If this condition is true, it means ‘i’ has no divisors other than 1 and itself, making it a prime number, and it will be printed.