The document discusses key concepts in number theory including natural numbers, divisibility, factors and multiples, prime and composite numbers, and divisibility tests. It defines natural numbers as the set of counting numbers {1,2,3,4...} and notes that number theory deals with studying the properties of these numbers, with a focus on divisibility. Divisibility is defined as one number being divisible by another if dividing the first by the second leaves no remainder. Factors are numbers that divide another number, while multiples are numbers that are divisible by another number. Prime numbers have only 1 and themselves as factors, while composite numbers have more than two factors. Divisibility tests provide ways to determine if one number is divisible by

1. Number Theory Yolanda McHenry, Ashley Courtney, Tyler Williams, Jamiya Hagger

5. Prime and Composite Numbers

9. Divisibility Tests(cont’d) The last digit,8, is an even number therefore the 123,216 is divisible by 2. 123,216 The sum of the digits,15, is divisible by 3 therefore 123,216 is divisible by 3. The last two digits 16, are divisible by 4 therefore 123,216 is divisible by 4. 3 Sum of the digits is divisible by 3. 4 Last two digits for a number divisible by 4.