First prime number in range python

A prime number is a natural number which is greater than 1 and has no positive divisor other than 1 and itself, such as 2, 3, 5, 7, 11, 13, and so on.

The user is given two integer numbers, lower value, and upper value. The task is to write the Python program for printing all the prime numbers between the given interval (or range).

To print all the prime numbers between the given interval, the user has to follow the following steps:

• Step 1: Loop through all the elements in the given range.
• Step 2: Check for each number if it has any factor between 1 and itself.
• Step 3: If yes, then the number is not prime, and it will move to the next number.
• Step 4: If no, it is the prime number, and the program will print it and check for the next number.
• Step 5: The loop will break when it is reached to the upper value.

Example: The Python Code to Print the Prime Number between the given Interval.

Output:

Please, Enter the Lowest Range Value:  14
Please, Enter the Upper Range Value:  97
The Prime Numbers in the range are: 
17
19
23
29
31
37
41
43
47
53
59
61
67
71
73
79
83
89
97

Conclusion

In this tutorial, we have shown how to write the code to print the prime numbers between the given interval of numbers.

Given two integer as Limits, low and high, the objective is to write a code to in Python Find Prime Numbers in a Given Range in Python Language. To do so we’ll use nested loops to check for the Prime while Iterating through the range.

Example
Input : low = 2 , high = 10
Output : 2 3 5 7

Prime Numbers A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself.

Method 1: Using inner loop Range as [2, number-1]

Working

For two integer inputs as low and high limits of the interval,

• Run a for loop to iterate through all the numbers.
• Run a Nested for loop to check for prime or not.

Let’s implement the above logic in Python Language.

Python Code

Run

# python find prime numbers in range 
low, high = 2, 10
primes = []

for i in range(low, high + 1):
    flag = 0

    if i < 2:
        continue
    if i == 2:
        primes.append(2)
        continue

    for x in range(2, i):
        if i % x == 0:
            flag = 1
            break

    if flag == 0:
        primes.append(i)
        
print(primes)

Method 2: Using inner loop Range as [2, number/2]

Working

For two integer inputs as limits, we perform the following main operations,

• Run a for loop to iterate through the numbers in a given interval.
• Run a nested while to check for prime by checking if the number has any other factors in the range [2, number/2].

Let’s implement the above logic in Python Language.

Python Code

Run

low, high = 2, 10
primes = [2]

for num in range(low, high + 1):
    flag = 0
    if num < 2:
        flag = 1
        
    if num % 2 == 0:
        continue
    iter = 2

    while iter < int(num / 2):
        if num % iter == 0:
            flag = 1
            break
        iter += 1

    if flag == 0:
        primes.append(num)

print(primes)

Method 3: Using inner loop Range as [2, sqrt(number)]

Working

For two integer inputs as low and high limits of the interval, we perform the following

• Run a for loop to iterate through the number in the given interval.
• Run a nested while loop to check for prime or not.
• We do so by checking if the number has any factors in the range [2, sqrt(number)].

Let’s implement the above logic in Python Language.

Python Code

Run

low, high = 2, 10
primes = [2, 3]

for num in range(low, high + 1):
    flag = 0
    
    if num < 2:
        flag = 1
        
    if num % 2 == 0:
        continue
        
    if num % 3 == 0:
        continue
        
    iter = 2
    while iter < int(pow(num, 0.5)):
        if num % iter == 0:
            flag = 1
            break
        iter += 1
        
    if flag == 0:
        primes.append(num)

print(primes)

Method 4: Using inner loop Range as [3, sqrt(number), 2]

Working

This method is similar to the one above but here we’ll use 2 as a step to skip the even numbers.

For a given interval as [low, high], we do the following

• Run a for loop to iterate through the numbers that lay in the input interval.
• Run a nest while eith step size as 2 from 3 to the square root of number and check for factors of the number in that interval.

Let’s implement the above logic in Python Language.

Python Code

Run

low, high = 2, 10
primes = [2, 3]

for num in range(low, high + 1):
    flag = 0
    if num < 2:
        flag = 1

    if num % 2 == 0:
        continue
        
    if num % 3 == 0:
        continue

    iter = 3

    while iter < int(pow(num, 0.5)):
        if num % iter == 0:
            flag = 1
            break
        iter += 2

    if flag == 0:
        primes.append(num)

print(primes)

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