$list of prime numbers up to 100 million$

Without it, you could take “has two factors, 1 and itself” as being true for 1, since 1 and itself are both factors and there is no other. This is where the word “exactly” comes in.

Prime numbers have EXACTLY two factors, not 'at most two' or anything like that. So we say that 29 is a prime number, but 28 isn't.Īs we’ll be seeing in the next two weeks, there are many ways to misstate this definition every word in the definition matters! Note that the definition of a prime number doesn't allow 1 to be a prime number: 1 only has one factor, namely 1.

If we list the factors of 29, we only have 1 and 29. For example, if we list the factors of 28, we have 1, 2, 4, 7, 14, and 28. We’ll start with an anonymous question from 1995: Prime Numbersĭoctor Ken answered with the definition and a pair of examples: Hello!Ī prime number is a positive number that has exactly two factors, 1 and itself. I’ll begin a short series of posts on prime numbers with several questions on the basics: What are prime (and composite) numbers, and why do they matter?

List of prime numbers up to 100 million