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<!DOCTYPE html>
<html lang=en>
<head>
  <meta charset=utf-8>
  <title>Magic number — single</title>
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<body>
  <h1>Magic number check</h1>
  <p>Edit <code>number</code>, then <strong>Run</strong>.</p>
  <pre id=out></pre>
  <script>document.getElementById("out").textContent=function(t){for(;t>9;){for(var e=0;t>0;)e+=t%10,t=Math.floor(t/10);t=e}return 1===t}(19)?"19 is a Magic Number.":"19 is not a Magic Number."</script>
</body>
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JavaScript Magic Number — Single value (Try It)