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### Finding Prime Numbers

```
Date: 12/5/95 at 9:44:6
From: Anonymous
Subject: prime numbers

What is the easiest way to find a prime number?
```

```
Date: 12/14/95 at 23:0:26
From: Doctor Ken
Subject: Re: prime numbers

Hello!

Actually, it can pretty hard to figure out whether a given number is
prime.  In fact, the toughest secret codes in the world rely on the fact
that it's really hard (even for a computer) to factor big numbers.
These are numbers that have somewhere around 30 digits.

For smaller numbers, it's a little easier to figure out, but you
basically  have to go through your list of known prime numbers
(2,3,5,7,11,13,...) and check to see whether any of them divide
the number you have.  It can get pretty slow, but it's pretty easy
and it works.  There are some faster (and much harder!) ways to do it,
but they don't always work.

Here are all the prime numbers up to 500:

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67,
71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139,
149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223,
227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293,
307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383,
389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463,
467, 479, 487, 491, 499, ...

-Doctor Ken,  The Geometry Forum

```
Associated Topics:
Middle School Prime Numbers

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