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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS Number Pattern 18 - Try It (Browser)</title>
</head>
<body>
  <h1>Alternating Odd-Even Row Pattern (document.write)</h1>
  <p>Edit loop limits, then click Run.</p>

  <script>
    for (let i = 1; i <= 5; i++) {
      let k = i % 2 === 0 ? 2 : 1;
      for (let j = 1; j <= i; j++) {
        document.write(k + " ");
        k += 2;
      }
      document.write("<br>");
    }
  </script>
</body>
</html>

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JavaScript Number Pattern 18 (Try It — Browser)