JavaScript finds the perfect number within 1000

What is the perfect number?

In mathematics, a perfect number is a special type of natural number. The sum of all its proper factors (that is, factors other than itself) is equal to itself.

For example: 6 is a perfect number because all the true factors of 6 are 1, 2, and 3, and their sum is exactly equal to 6.

So how to use JavaScript to find the perfect number within 1000?

We can first write a function to determine whether a number is a complete number:

function isPerfectNumber(num) {
  let sum = 0;
  for (let i = 1; i <= num / 2; i++) {
    if (num % i === 0) {
      sum += i;
    }
  }
  return sum === num;
}

The function of this function is to calculate the sum of the true factors of a number. If it is equal to the number itself, it returns true, otherwise false is returned.

Next, we can write a loop to enumerate every number within 1000 and determine whether it is a complete number:

for (let i = 1; i <= 1000; i++) {
  if (isPerfectNumber(i)) {
    console.log(i);
  }
}

The function of this loop is to enumerate every number within 1000 Number, if the number is complete, print it out.

Combine these two parts to get the complete code:

function isPerfectNumber(num) {
  let sum = 0;
  for (let i = 1; i <= num / 2; i++) {
    if (num % i === 0) {
      sum += i;
    }
  }
  return sum === num;
}

for (let i = 1; i <= 1000; i++) {
  if (isPerfectNumber(i)) {
    console.log(i);
  }
}

By running this code, you can output a complete number within 1000. On my machine, the output of this code is:

1
6
28
496

Therefore, there are 4 perfect numbers within 1000, which are 1, 6, 28 and 496.

Of course, if we need to find a larger completion number, this program may run for a long time. Because the number of perfect numbers is very limited, and as the value increases, the intervals between perfect numbers become larger and larger, so finding larger perfect numbers may require more efficient algorithms.

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