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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Amicable partner finder</title>
</head>
<body>
  <h1>Find amicable partner of a</h1>
  <p>Edit <code>a</code> in the script, then click <strong>Run</strong>.</p>
  <pre id="out"></pre>
  <script>
    (function () {
      function properDivisorSum(num) {
        if (num <= 1) return 0;
        var total = 0;
        for (var i = 1; i <= Math.floor(num / 2); i++) {
          if (num % i === 0) total += i;
        }
        return total;
      }
      function amicablePartner(a) {
        var b = properDivisorSum(a);
        if (a !== b && properDivisorSum(b) === a) return b;
        return null;
      }
      var a = 220;
      var partner = amicablePartner(a);
      var msg = partner !== null
        ? "Partner of " + a + " is " + partner + "."
        : a + " has no amicable partner.";
      document.getElementById("out").textContent = msg;
    })();
  </script>
</body>
</html>

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JavaScript Amicable Partner — Find partner (Try It)