nth prime number python: In the previous article, we have discussed Python Program to Delete Random Item from a List
Prime Number :
A prime number is one that can only be divided by one and itself.
Given a number ‘n’, and the task to find the nth prime number.
Examples:
Example1:
Input:
Given number = 8
Output:
The above given nth Prime Number is = 19
Example2:
Input:
Given number = 3
Output:
The above given nth Prime Number is = 5
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Program to Find nth Prime Number
Below are the ways to find the nth prime number.
Method #1: Using While, For Loop (Static Input)
Approach:
- Give the number say ‘n’ as static input and store it in a variable.
- Take a list say ‘prime_numbers’ and initialize it with 2, 3 values.
- Take a variable and initialize it with 3 say ‘x’.
- Check if the given number is between greater than 0 and less than 3 using the if conditional statement.
- If the statement is true, then print the value of the list “prime_numbers[n-1] “.
- Check if the given number is greater than 2 using the elif conditional statement.
- Iterate the loop infinite times using the while loop i.e while(True).
- Inside the loop increment the value of the above given ‘x’ variable by ‘1’.
- Take a variable to say ‘y’ and initialize with ‘True’.
- Loop from 2 to int((x/2)+1) using the for loop and int function().
- Check if the value of variable ‘x’ modulus iterator value is equal to zero or not using the if conditional statement.
- If the statement is true, assign “False” to the variable y, break the statement and come out of the loop.
- Check if variable y is equal to True using the if conditional statement.
- If the statement is true, then append the value of variable ‘x’ to the above list ‘prime_numbers’.
- Check if the length of the above list ‘prime_numbers’ is equal to the given number.
- If the statement is true, then give a break statement and come out of the while loop.
- Print the value of the list “prime_numbers[n-1]” to get the nth prime number.
- Else print “Invalid number. Please enter another number “.
- The Exit of the Program.
Below is the implementation:
# Give the number say 'n' as static input and store it in a variable.
num = 5
# Take a list say 'prime_numbers' and initialize it with 2, 3 values.
prim_numbrs = [2, 3]
# Take a variable and initialize it with 3 say 'x'.
x = 3
# Check if the given number is between greater than 0 and less than 3 using the if
# conditional statement.
if(0 < num < 3):
# If the statement is true, then print the value of the list "prime_numbers[n-1] ".
print('The above given nth Prime Number is =', prim_numbrs[num-1])
# Check if the given number is greater than 2 using the elif conditional statement.
elif(num > 2):
# Iterate the loop infinite times using the while loop i.e while(True).
while (True):
# Inside the loop increment the value of the above given 'x' variable by '1'.
x += 1
# Take a variable say 'y' and initialize with 'True'.
y = True
# Loop from 2 to int((x/2)+1) using the for loop and int function().
for itr in range(2, int(x/2)+1):
# Check if the value of variable 'x' modulus iterator value is equal to zero or not
# using the if conditional statement.
if(x % itr == 0):
# If the statement is true, assign "False" to the variable y, break the statement and
# come out of the loop.
y = False
break
# Check if variable y is equal to True using the if conditional statement.
if(y == True):
# If the statement is true, then append the value of variable 'x' to the
# above list 'prime_numbers'.
prim_numbrs.append(x)
# Check if the length of the above list 'prime_numbers' is equal to the given number.
if(len(prim_numbrs) == num):
# If the statement is true, then give a break statement and come out of the while loop.
break
# Print the value of the list "prime_numbers[n-1]" to get the nth prime number.
print('The above given nth Prime Number is = ', prim_numbrs[num-1])
# Else print "Invalid number. Please enter another number ".
else:
print("Invalid number. Please enter another number ")
Output:
The above given nth Prime Number is = 11
Method #2: Using While, For Loop (User Input)
Approach:
- Give the number say ‘n’ as user input using int(input()) and store it in a variable.
- Take a list say ‘prime_numbers’ and initialize it with 2, 3 values.
- Take a variable and initialize it with 3 say ‘x’.
- Check if the given number is between greater than 0 and less than 3 using the if conditional statement.
- If the statement is true, then print the value of the list “prime_numbers[n-1] “.
- Check if the given number is greater than 2 using the elif conditional statement.
- Iterate the loop infinite times using the while loop i.e while(True).
- Inside the loop increment the value of the above given ‘x’ variable by ‘1’.
- Take a variable to say ‘y’ and initialize with ‘True’.
- Loop from 2 to int((x/2)+1) using the for loop and int function().
- Check if the value of variable ‘x’ modulus iterator value is equal to zero or not using the if conditional statement.
- If the statement is true, assign “False” to the variable y, break the statement and come out of the loop.
- Check if variable y is equal to True using the if conditional statement.
- If the statement is true, then append the value of variable ‘x’ to the above list ‘prime_numbers’.
- Check if the length of the above list ‘prime_numbers’ is equal to the given number.
- If the statement is true, then give a break statement and come out of the while loop.
- Print the value of the list “prime_numbers[n-1]” to get the nth prime number.
- Else print “Invalid number. Please enter another number “.
- The Exit of the Program.
Below is the implementation:
# Give the number say 'n' as user input using int(input()) and store it in a variable.
num = int(input("Enter some random number = "))
# Take a list say 'prime_numbers' and initialize it with 2, 3 values.
prim_numbrs = [2, 3]
# Take a variable and initialize it with 3 say 'x'.
x = 3
# Check if the given number is between greater than 0 and less than 3 using the if
# conditional statement.
if(0 < num < 3):
# If the statement is true, then print the value of the list "prime_numbers[n-1] ".
print('The above given nth Prime Number is =', prim_numbrs[num-1])
# Check if the given number is greater than 2 using the elif conditional statement.
elif(num > 2):
# Iterate the loop infinite times using the while loop i.e while(True).
while (True):
# Inside the loop increment the value of the above given 'x' variable by '1'.
x += 1
# Take a variable say 'y' and initialize with 'True'.
y = True
# Loop from 2 to int((x/2)+1) using the for loop and int function().
for itr in range(2, int(x/2)+1):
# Check if the value of variable 'x' modulus iterator value is equal to zero or not
# using the if conditional statement.
if(x % itr == 0):
# If the statement is true, assign "False" to the variable y, break the statement and
# come out of the loop.
y = False
break
# Check if variable y is equal to True using the if conditional statement.
if(y == True):
# If the statement is true, then append the value of variable 'x' to the
# above list 'prime_numbers'.
prim_numbrs.append(x)
# Check if the length of the above list 'prime_numbers' is equal to the given number.
if(len(prim_numbrs) == num):
# If the statement is true, then give a break statement and come out of the while loop.
break
# Print the value of the list "prime_numbers[n-1]" to get the nth prime number.
print('The above given nth Prime Number is = ', prim_numbrs[num-1])
# Else print "Invalid number. Please enter another number ".
else:
print("Invalid number. Please enter another number ")
Output:
Enter some random number = 1 The above given nth Prime Number is = 2
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