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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS Number Pattern 27 - Try It (Browser)</title>
</head>
<body>
  <h1>Palindromic Number Triangle (document.write)</h1>
  <p>Edit <code>rows</code>, then click Run.</p>

  <script>
    var rows = 5;
    for (var i = 1; i <= rows; i++) {
      for (var j = 1; j <= i; j++)
        document.write(j);
      for (var k = i - 1; k >= 1; k--)
        document.write(k);
      document.write("<br>");
    }
  </script>
</body>
</html>

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JavaScript Number Pattern 27 (Try It — Browser)