Python Program to Print Series 1, -2, 6, -15, 31 ... N

In the previous article, we have discussed Python Program to Print Series 1, 3, 7, 15, 31 … N
Given a number N and the task is to print the series (1, -2, 6, -15, 31 … N) till the given number N in Python.

Examples:

Example1:

Input:

Given Number (Limit) = 8

Output:

The above series till the given number{ 8 } is :
1 -2 6 -15 31 -56 92 -141

Example2:

Input:

Given Number (Limit) = 11

Output:

The above series till the given number{ 11 } is :
1 -2 6 -15 31 -56 92 -141 205 -286 386

Program to Print Series 1, -2, 6, -15, 31 … N in Python

Below are the ways to print the series (1, -2, 6, -15, 31 … N) till the given number N in Python :

Using While Loop (Static Input)
Using While loop (User Input)

Method #1: Using While Loop (Static Input)

Approach:

Give the number N (Limit) as static input and store it in a variable.
Take a variable to say itr and initialize its value to 1.
Take another variable say previous_val and initialize its value to 1.
Loop until the above-declared variable itr value is less than or equal to the given number using the while loop.
Inside the loop, check if the above itr value is even or not using the if conditional statement.
If it is true, then print the value of above previous_val multiplied with -1 separated by spaces.
Else, Print the value of the above previous_val separated by spaces.
Calculate the value of itr raised to power 2 using the pow() function and add it to the previous_val.
Store it in the same variable previous_val.
Increment the above itr value by 1.
The Exit of the Program.

Below is the implementation:

# Give the number N (Limit) as static input and store it in a variable.
gvn_numb = 8
# Take a variable to say itr and initialize its value to 1.
itr = 1
# Take another variable say previous_val and initialize its value to 1.
previous_val = 1
print("The above series till the given number{", gvn_numb, "} is :")
# Loop until the above-declared variable itr value is less than or equal to the
# given number using the while loop.
while itr <= gvn_numb:
   # Inside the loop, check if the above itr value is even or not using the if
   # conditional statement.
    if(itr % 2 == 0):
         # If it is true, then print the value of above previous_val multiplied with -1
         # separated by spaces.
        print(-1*previous_val, end=" ")
    else:
        # Else, Print the value of the above previous_val separated by spaces.
        print(previous_val, end=" ")
   # Calculate the value of itr raised to power 2 using the pow() function and
   # add it to the previous_val.
   # Store it in the same variable previous_val.
    previous_val += pow(itr, 2)
    # Increment the above itr value by 1.
    itr += 1

Output:

The above series till the given number{ 8 } is :
1 -2 6 -15 31 -56 92 -141

Method #2: Using While loop (User Input)

Approach:

Give the number N (Limit) as user input using the int(input()) function and store it in a variable.
Take a variable to say itr and initialize its value to 1.
Take another variable say previous_val and initialize its value to 1.
Loop until the above-declared variable itr value is less than or equal to the given number using the while loop.
Inside the loop, check if the above itr value is even or not using the if conditional statement.
If it is true, then print the value of above previous_val multiplied with -1 separated by spaces.
Else, Print the value of the above previous_val separated by spaces.
Calculate the value of itr raised to power 2 using the pow() function and add it to the previous_val.
Store it in the same variable previous_val.
Increment the above itr value by 1.
The Exit of the Program.

Below is the implementation:

# Give the number N (Limit) as user input using the int(input()) function and 
# store it in a variable.
gvn_numb = int(input("Enter some Random Number = "))
# Take a variable to say itr and initialize its value to 1.
itr = 1
# Take another variable say previous_val and initialize its value to 1.
previous_val = 1
print("The above series till the given number{", gvn_numb, "} is :")
# Loop until the above-declared variable itr value is less than or equal to the
# given number using the while loop.
while itr <= gvn_numb:
   # Inside the loop, check if the above itr value is even or not using the if
   # conditional statement.
    if(itr % 2 == 0):
         # If it is true, then print the value of above previous_val multiplied with -1
         # separated by spaces.
        print(-1*previous_val, end=" ")
    else:
        # Else, Print the value of the above previous_val separated by spaces.
        print(previous_val, end=" ")
   # Calculate the value of itr raised to power 2 using the pow() function and
   # add it to the previous_val.
   # Store it in the same variable previous_val.
    previous_val += pow(itr, 2)
    # Increment the above itr value by 1.
    itr += 1

Output:

Enter some Random Number = 11
The above series till the given number{ 11 } is :
1 -2 6 -15 31 -56 92 -141 205 -286 386

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