<p>Okay so the question is..</p>
<p>How many integers greater than 20 and less than 30 are each the product of exactly two different numbers, both of which are prime.
A. 0
B. 1
C. 2
D. 3
E. 4</p>
<p>Now they say it's 3 because there is 21 (3<em>7), 22 (2</em>11), and 26 (2*13).</p>
<p>But what I don't get is why isn't 23 because it's 23*1=23 which is two prime numbers multiplying to get a prime??? Same with 29. Can someone please explain why the answer is 3.</p>
<p>What’s the definition of a [prime</a> number](<a href=“http://en.wikipedia.org/wiki/Prime_number]prime”>Prime number - Wikipedia)? :)</p>
<p>1 isn’t prime.</p>
<p>By definition, 1 isn’t prime. If it was prime, then 23 could be written as the product of at least two prime numbers (23<em>1 or 23</em>1*1) and “prime number” wouldn’t mean anything anymore.</p>
<p>Oh wow, well I feel like an idiot, haha. Thanks guys. I don’t know why I was thinking 1 was prime.</p>
<p>Well, 1 = 1*1 and it is a product of 1 and itself. But then 2,3,5,… would be composite numbers.</p>