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							Sum of the Series 1! + 2! + ... + n!
								Certification: Basic Level
								Accuracy: 53.33%
								Submissions: 15
								Points: 10
							
							Write a C++ program to calculate the sum of the series 1! + 2! + 3! + ... + n!, where n! represents the factorial of n.
Example 1
- Input: n = 5
- Output: 153
- Explanation: - Step 1: Calculate the factorials for each number from 1 to 5.
- Step 2: 1! = 1, 2! = 2, 3! = 6, 4! = 24, 5! = 120.
- Step 3: Sum = 1! + 2! + 3! + 4! + 5! = 1 + 2 + 6 + 24 + 120 = 153.
 
Example 2
- Input: n = 3
- Output: 9
- Explanation: - Step 1: Calculate the factorials for each number from 1 to 3.
- Step 2: 1! = 1, 2! = 2, 3! = 6.
- Step 3: Sum = 1! + 2! + 3! = 1 + 2 + 6 = 9.
 
Constraints
- 1 ≤ n ≤ 20
- Time Complexity: O(n), where n is the input number
- Space Complexity: O(1)
- The result may be large, so use long long int for calculations
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Solution Hints
- Calculate the factorial of each number from 1 to n.
- Keep a running sum of factorials.
- Be careful about integer overflow for larger values of n.
- You can optimize by calculating each factorial based on the previous one instead of recalculating from scratch.
