viewing distance calculator

function calc1(form) {
  a = form.a.value;
  b = Math.round(Math.pow(Math.pow(a, 2)/1.31640624208984, .5)/2.97869411418791);
  c = Math.round(Math.pow(Math.pow(a, 2)/1.31640624208984, .5)/4.46804291661112);
  d = Math.round(Math.pow(Math.pow(a, 2)/1.31640624208984, .5)/6.70206437491669);
  e = Math.round(Math.pow(Math.pow(a, 2)/1.31640624208984, .5)/13.9626341144098);
  f = Math.round(Math.pow(Math.pow(a, 2)/1.31640624208984, .5)/27.9252682288196);
  form.total1.value = b;
  form.total2.value = c;
  form.total3.value = d;
  form.total4.value = e;
  form.total5.value = f;
}


<form>Enter screen size:<input name="a" size="3" type="number" autocomplete="off"> inches diagonal <input type="button" value="Calculate" onclick="calc1(this.form)"><p></p>
<ul>
<li>For <strong>480p</strong> (720×480) resolution, you must sit:<br>
<input maxlength="40" name="total1" size="3" type="text"> feet <em>or closer</em> to see all available detail</li>
<li>For <strong>720p</strong> (1280×720) resolution, you must sit:<br>
<input maxlength="40" name="total2" size="3" type="text"> feet <em>or closer</em> to see all available detail</li>
<li>For <strong>1080p</strong> (1920×1080) resolution, you must sit:<br>
<input maxlength="40" name="total3" size="3" type="text"> feet <em>or closer</em> to see all available detail</li>
<li>For <strong>4k</strong> (3840×2160) resolution, you must sit:<br>
<input maxlength="40" name="total4" size="3" type="text"> feet <em>or closer</em> to see all available detail</li>
<li>For <strong>8k</strong> (7680×4320) resolution, you must sit:<br>
<input maxlength="40" name="total5" size="3" type="text"> feet <em>or closer</em> to see all available detail</li>
</ul>
</form>

Hi,

Sorry to bug you but I'm messing around with a distance calculator (more to understand how it works - hobbyist) and I'm struggling to figure out where these much needed numbers are generated from

1.31640624208984, 5, 4.46804291661112, 6.70206437491669, 13.9626341144098 and 27.9252682288196

Any points towards the right direction would be greatly appreciated

Cheers, Shane