What You'll Learn
- •Using mathematical formulas for summation
- •Applying integer division for exact results
- •Validating that N is positive
Python
# Program to find the sum of first N natural numbers
n = int(input("Enter a positive integer N: "))
if n <= 0:
print("Please enter a positive integer.")
else:
total = n * (n + 1) // 2
print("Sum of first", n, "natural numbers is:", total)Output
Enter a positive integer N: 10 Sum of first 10 natural numbers is: 55
We use the well-known formula:
[ 1 + 2 + 3 + \dots + N = \frac{N(N+1)}{2} ]
Using integer division // ensures we get an integer result when N is an integer.
Step-by-Step Breakdown
- 1Read N from the user.
- 2Check that N is positive.
- 3Apply the formula N * (N + 1) // 2.
- 4Print the resulting sum.