46 Part 1: The World of Numbers
Prime Numbers
When you multiply 1 by any number, the product is that number. 1 v 4 = 4, 1 v 17 = 17, and
1 v 132 = 132. The number 1 is a factor of any number. When you write a multiplication
problem like those, with 1 as a factor, the other factor is always the same as the product. So if 1
is a factor of 4, then 4 is also a factor of 4, and that’s the case for any number. Any number v 1 =
that number. The number 1 is a factor of every number, and every number is a factor of itself.
Every number can be written as itself times 1.
All that multiplying by 1 may seem boring, and many numbers have other factors that make more
interesting problems. The number 6, in addition to being 1 v 6 is also equal to 2 v 3. And some
numbers have lots of possible factors. 24 could be 1 v 24, 2 v 12, 3 v 8, or 4 v 6. But there are
numbers that only have one set of factors. Numbers whose only possible factors are themselves
and 1 are called prime numbers. Numbers that have other possible factors besides themselves and
1 are called composite numbers. You might think that only small numbers like 2 and 3 are prime
numbers, but that’s not the case.DEFINITION
A prime number is a whole number whose only factors are itself and 1. A composite
number is a whole number that is not prime because it has factors other than itself
and 1.You can use blocks to help you visualize this concept. If you have a prime number of blocks,
there’s only one rectangle you can make. Try to rearrange and you just can’t get a rectangle.The number 7 is a prime number.With a composite number of blocks, you can always make at least two rectangles.The number 8 is a composite number.12345671234
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