# JavaScript: Find a perfect number

## JavaScript Function: Exercise-12 with Solution

Write a JavaScript function which says whether a number is perfect.

**Note :** According to Wikipedia : In number theory, a perfect number is a positive integer that is equal to the sum of its proper positive divisors, that is, the sum of its positive divisors excluding the number itself (also known as its aliquot sum). Equivalently, a perfect number is a number that is half the sum of all of its positive divisors (including itself).

*Example* : The first perfect number is 6, because 1, 2, and 3 are its proper positive divisors, and 1 + 2 + 3 = 6. Equivalently, the number 6 is equal to half the sum of all its positive divisors: ( 1 + 2 + 3 + 6 ) / 2 = 6. The next perfect number is 28 = 1 + 2 + 4 + 7 + 14. This is followed by the perfect numbers 496 and 8128.

**Pictorial Presentation:**

**Sample Solution**: -

**HTML Code:**

```
<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Find a perfect number</title>
</head>
<body>
</body>
</html>
```

**JavaScript Code:**

```
function is_perfect(number)
{
var temp = 0;
for(var i=1;i<=number/2;i++)
{
if(number%i === 0)
{
temp += i;
}
}
if(temp === number && temp !== 0)
{
console.log("It is a perfect number.");
}
else
{
console.log("It is not a perfect number.");
}
}
is_perfect(28);
```

Sample Output:

It is a perfect number.

**Flowchart: **

**Live Demo: **

See the Pen JavaScript - Find a perfect number-function-ex- 12 by w3resource (@w3resource) on CodePen.

**Improve this sample solution and post your code through Disqus**

**Previous:** Write a JavaScript function which will take an array of numbers stored and find the second lowest and second greatest numbers, respectively.

**Next:** Write a JavaScript function to compute the factors of a positive integer.

**What is the difficulty level of this exercise?**

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## JavaScript: Tips of the Day

**Shorten an array using its length property**

A great way of shortening an array is by redefining its length property.

let array = [0, 1, 2, 3, 4, 5, 6, 6, 8, 9] array.length = 4 // Result: [0, 1, 2, 3]

Important to know though is that this is a destructive way of changing the array. This means you lose all the other values that used to be in the array.

Ref: https://bit.ly/2LBj213

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