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<html lang=en>
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  <meta charset=utf-8>
  <title>Pronic numbers in range</title>
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<body>
  <h1>Pronic numbers in the range 1 to 20</h1>
  <pre id=out></pre>
  <script>!function(){function n(n){if(n<0)return!1;for(let t=0;;t++){const r=t*(t+1);if(r===n)return!0;if(r>n)return!1}}var t,r=[];for(t=1;t<=20;t++)n(t)&&r.push(String(t));var e=[];e.push("Pronic numbers in the range 1 to 20:"),e.push(r.join(" ")),document.getElementById("out").textContent=e.join("\n")}()</script>
</body>
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JavaScript Pronic Number — Range 1 to 20 (Try It)