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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS Number Pattern 20 - Try It (Browser)</title>
</head>
<body>
  <h1>Continuous Number Triangle (document.write)</h1>
  <p>Edit loop limits, then click Run.</p>

  <script>
    let k = 1;

    for (let i = 1; i <= 4; i++) {
      for (let j = 1; j <= i; j++) {
        document.write(k++ + " ");
      }
      document.write("<br>");
    }
  </script>
</body>
</html>

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JavaScript Number Pattern 20 (Try It — Browser)