PHP Exercises: Compute the sum of first n given prime numbers
65. Sum of First n Prime Numbers
Write a PHP program to compute the sum of first n given prime numbers.
Input: n ( n ≤ 10000). Input 0 to exit the program.
Pictorial Presentation:

Sample Solution:
PHP Code:
Explanation:
- Set Maximum Prime Value:
- The variable $max is set to 105000, which will be the upper limit for the prime numbers to be calculated.
- Create Prime Flag Array:
- A fixed-size array $arr is created using \SplFixedArray, with a size of max + 1. This array will hold flags indicating whether each number is prime.
- Initialize Array:
- A for loop initializes the array values from 2 to max to 1, indicating that all numbers are initially considered prime.
- Sieve of Eratosthenes Algorithm:
- The algorithm starts with i set to 2 and loops up to the square root of $max.
- If the current number is marked as prime (i.e., arr[$i] is 1), it enters another loop to mark its multiples as non-prime (0).
- This is done by iterating j and setting arr[$i * $j] to 0 for multiples of i.
- Input Processing Loop:
- The code reads input from standard input until the input '0' is encountered.
- Each input line is trimmed and converted to an integer $n.
- Initialize Variables for Summation:
- Two variables, $result and $cnt, are initialized to 0. $result will store the sum of prime numbers, and $cnt will count how many prime numbers have been found.
- • Find and Sum First N Prime Numbers:
- A for loop iterates through the array of numbers from 2 to max.
- If the count of found primes ($cnt) equals $n, the loop breaks.
- If the current number is prime (i.e., arr[$i] is 1), it is added to $result, and $cnt is incremented.
- Output the Result:
- After summing the required prime numbers, the code outputs the result, indicating the sum of the first n prime numbers.
Sample Input:
25
0
Sample Output:
Sum of first 25 prime numbers:1060
Flowchart:

For more Practice: Solve these Related Problems:
- Write a PHP script to generate and sum the first n prime numbers using iterative methods.
- Write a PHP function to validate input and calculate the cumulative sum of the first n prime numbers recursively.
- Write a PHP script to produce the first n primes and then compute their total using array operations.
- Write a PHP script to verify the summation of prime numbers using both loop iteration and mathematical validation.
PHP Code Editor:
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Previous: Write a PHP program to replace a string "Python" with "PHP" and "Python" with " PHP" in a given string.
Next: Write a PHP program that accept a even number (n should be greater than or equal to 4 and less than or equal to 50000, Goldbach number) from the user and create a combinations that express the given number as a sum of two prime numbers. Print the number of combinations.
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