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In number theory, a deficient number is a number in which the sum of its proper factors is less than the number.  Examples explaining what a deficient number is. For example, the number 4 is deficient. The proper factors of 4 are 1 and 2. Since 1 + 2 = 3 and 3 is smaller…

This lesson presents divisibility rules, also called divisibility tests, for the numbers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 13. Divisibility rules of whole numbers are very useful because they help us to quickly determine if a given number can be divided by 2, 3, 4, 5, 6, 7, 8,…

This prime numbers chart displays all prime numbers from 1 to 100 in red.Do not try to learn this prime numbers chart by heart. A prime numbers chart should only be used as a quick reference. If the prime numbers chart does not have the number you are looking for, use this prime number calculator to quickly…

For example, 7 is a prime number because 7 is only divisible by 1 and 7. This means that if you divide 7 by a number that is not 1 or 7, you will not get a remainder of zero.  7 divided by 1 gives a remainder of 0 since 7 = 1 × 7 + 0 7 divided by 2 gives a remainder of 1 since…

This lesson will teach you 3 methods for finding the least common multiple (LCM) of two whole numbers. We will start with a definition of the word multiple. The multiples of a number are the answers that you get when you multiply that number by the whole numbers except 0. Remember that the whole numbers…

The factors of 20 are the numbers 1, 2, 4, 5, 10, 20, -1, -2, -4, -5, -10, and -20. As you can see, the total number of factors 20 has is 12. Make the following observations! How to easily find the factors of 20 By definition, the numbers a and b are called factors of ab and…

Counting factors is really useful when you are looking for the factors of a number. You may need this information if you do not want to miss any factors. To count factors, first we need to get the prime factorization of the number. Example #1: How many factors does 8 have?8 = 2 × 2…

The greatest common factor (GCF) is the largest factor of two numbers. An understanding of factor is important in order to understand the meaning of GCF. What are factors? When two or more numbers are multiplied in a multiplication problem, each number is a factor in the multiplication. Take a look at the following multiplication…

Get a strong understanding of the very basic of number theory. Life is full of patterns, but oftentimes, we do not realize as much as we should that mathematics too is full of patterns. Number theory is a branch of pure mathematics that explore the patterns and properties we see when dealing with positive integers. If…