Python Program to Read a Number n And Print the Series "1+2+.....+n=

When it is required to display the sum of all natural numbers within a given range and show the series format "1+2+...+n=sum", we can create a program that builds the series string and calculates the sum.

Below is a demonstration of the same ?

Method 1: Using Loop to Build Series

Example

def print_series_sum(n):
    series = ""
    total = 0
    
    for i in range(1, n + 1):
        total += i
        if i == 1:
            series = str(i)
        else:
            series += "+" + str(i)
    
    return f"{series}={total}"

n = 5
print("The number is:")
print(n)
print("The series is:")
print(print_series_sum(n))

The number is:
5
The series is:
1+2+3+4+5=15

Method 2: Using Formula for Direct Calculation

Example

def print_series_with_formula(n):
    # Build series string
    series = "+".join(str(i) for i in range(1, n + 1))
    
    # Calculate sum using formula: n*(n+1)/2
    total = n * (n + 1) // 2
    
    return f"{series}={total}"

n = 7
print("The number is:")
print(n)
print("The series is:")
print(print_series_with_formula(n))

The number is:
7
The series is:
1+2+3+4+5+6+7=28

Method 3: Interactive Input Version

Example

def display_natural_sum():
    n = int(input("Enter a number: "))
    
    # Build and display the series
    series_parts = []
    total = 0
    
    for i in range(1, n + 1):
        series_parts.append(str(i))
        total += i
    
    series = "+".join(series_parts)
    print(f"{series}={total}")

# Call the function
display_natural_sum()

Comparison

How It Works

• The program builds a string showing the series "1+2+3+...+n"

• It calculates the sum of natural numbers from 1 to n

• The formula n*(n+1)/2 provides an efficient way to calculate the sum

• String joining methods like "+".join() create clean series output

• The final result displays both the series and its sum

Conclusion

Use the formula method for efficient calculation of large numbers. The loop method is better for understanding the concept and building the visual series representation.