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Updated on: 04 Jan 2022, 06:47
Originally posted by JeffTargetTestPrep on 03 Jan 2022, 14:05.
Last edited by JeffTargetTestPrep on 04 Jan 2022, 06:47, edited 1 time in total.
Last edited by JeffTargetTestPrep on 04 Jan 2022, 06:47, edited 1 time in total.
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Is 1 a Prime Number?
The number 1 is not a prime number. Because of the definition of a prime number and the function of the number 1 in number theory, which doesn’t allow 1 to be a prime number for mathematical reasons, 1 is not prime. The good news is that, on the GMAT, you do not need to know why one is not a prime number; you just need to memorize the fact that it is not.Let’s review the definition of a prime number:
A prime number is an integer greater than 1 that has no factors other than 1 and itself.
Since we already know that 1 is not a prime, we see that the first prime number (and the only even prime number) is 2, since the factors of 2 are 2 and 1. The first 5 prime numbers are 2, 3, 5, 7, and 11.
Composite numbers are whole numbers that have more than 2 factors. Some examples of composite numbers are 6 (because 6 has factors of 1, 2, 3, and 6) and 8 (because 8 has factors of 1, 2, 4, and 8). Note that no prime number is a composite number.
For the GMAT, you should memorize the first 25 prime numbers, so that if you are finding the prime factorization of a given number (more on this below), you will know when the factorization is complete.
Prime Factorization
If we ever need to see which prime numbers make a particular number, we follow the process of prime factorization. An easy way to find the prime factorization of a number is to find a number that evenly divides the original number and keep factoring the quotients until we are left with just prime numbers. A useful way to stay organized and efficient when doing prime factorization is to use a factor tree.To read the complete article, view my full article on Target Test Prep’s blog.
03 Jan 2022, 14:24
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Thanks Jeff for the refresher.
I’d like to add that all prime numbers except for 2 and 5 end in 1, 3, 7, or 9.
I think this additional info complements the topic nicely.
Posted from my mobile device
I’d like to add that all prime numbers except for 2 and 5 end in 1, 3, 7, or 9.
I think this additional info complements the topic nicely.
Posted from my mobile device
manifest22
Joined: 20 Jun 2021
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03 Jan 2022, 21:59
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I think there's an error - 72 is not a prime number!
