Project Euler Problems

• Problem 21 @Project Euler - *In Progress*

  • Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
    If d(a) = b and d(b) = a, where a b, then a and b are an amicable pair and each of a and b are called amicable numbers.

    For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.

    Evaluate the sum of all the amicable numbers under 10000.

  • The answer is ...

    Calculated in 4.1E-5 seconds

• The Code (fresh off the presses, displaying what was used above):

  <?php

$amicable = new Amicable;

class Amicable
{
    public function __construct () 
    {    
        // Start Timer
        $Timer = new CalcTimer;
        $Timer -> StartTimer(); 
        
        echo "<h3>The answer is ...<h3/>";
        // Stop Timer
        $Timer -> StopTimer();    
    }
}
?>