Find the Count of Numbers Which Are Not Special
<p>You are given 2 <strong>positive</strong> integers <code>l</code> and <code>r</code>. For any number <code>x</code>, all positive divisors of <code>x</code> <em>except</em> <code>x</code> are called the <strong>proper divisors</strong> of <code>x</code>.</p>

<p>A number is called <strong>special</strong> if it has exactly 2 <strong>proper divisors</strong>. For example:</p>

<ul>
	<li>The number 4 is <em>special</em> because it has proper divisors 1 and 2.</li>
	<li>The number 6 is <em>not special</em> because it has proper divisors 1, 2, and 3.</li>
</ul>

<p>Return the count of numbers in the range <code>[l, r]</code> that are <strong>not</strong> <strong>special</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">l = 5, r = 7</span></p>

<p><strong>Output:</strong> <span class="example-io">3</span></p>

<p><strong>Explanation:</strong></p>

<p>There are no special numbers in the range <code>[5, 7]</code>.</p>
</div>

<p><strong class="example">Example 2:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">l = 4, r = 16</span></p>

<p><strong>Output:</strong> <span class="example-io">11</span></p>

<p><strong>Explanation:</strong></p>

<p>The special numbers in the range <code>[4, 16]</code> are 4 and 9.</p>
</div>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= l &lt;= r &lt;= 10<sup>9</sup></code></li>
</ul>
Array; Math; Number Theory
const m = 31623

var primes [m + 1]bool

func init() {
	for i := range primes {
		primes[i] = true
	}
	primes[0] = false
	primes[1] = false
	for i := 2; i <= m; i++ {
		if primes[i] {
			for j := i * 2; j <= m; j += i {
				primes[j] = false
			}
		}
	}
}

func nonSpecialCount(l int, r int) int {
	lo := int(math.Ceil(math.Sqrt(float64(l))))
	hi := int(math.Floor(math.Sqrt(float64(r))))
	cnt := 0
	for i := lo; i <= hi; i++ {
		if primes[i] {
			cnt++
		}
	}
	return r - l + 1 - cnt
}