How to sort array by divisor sum faster?

I am sorting an array by divisor sum in ascending order. If two or more numbers have the same sum of divisors they have to be sorted in ascending order. The problem I have is that my version is not fast enough. Here is my code:

int divisorSum( double number )
{
    double sum = number + 1;
    for( int i = 2; i <= number / 2; i++ )
        if(( int )number % i == 0 )
            sum += i;
    return sum;
}
void sortByDivisorSum( double *array, int length )
{
    for( int i = 0; i < length; i++ )
    {
        for( int j = i + 1; j < length; j++ )
        {
            if(( divisorSum( array[ i ]) > divisorSum( array[ j ])) || (( divisorSum( array[ i ] ) == divisorSum( array[ j ])) && ( array[ i ] > array[ j ])))
            {
                array[ i ] += array[ j ];
                array[ j ] = array[ i ] - array[ j ];
                array[ i ] -= array[ j ];
            }
        }
    }
}
void readArrayy(double *array, int length)
{
    for(int index = 0; index < length; index++)
        scanf("%lf", &array[index]);
}
int main( void )
{
    int length, in;
    scanf( "%d", &length );
    double ar[ length ];
    readArrayy( ar, length );
    sortByDivisorSum( ar, length );
    for( in = 0; in < length; in++ )
    {
        printf( "%.0lf ", ar[in]);
    }
    return 0;
}

How to solve this in a faster way?

Input:

10
24 46 11 36 48 35 27 28 49 6

Output:

6 11 27 35 28 49 24 46 36 48