Difference between revisions of "Prime factorization"
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− | + | For a positive integer <math>n</math>, the '''prime factorization''' of <math>n</math> is an expression for <math>n</math> as a product of powers of [[prime number]]s. An important theorem of [[number theory]] called the [[Fundamental Theorem of Arithmetic]] tells us that every [[positive integer]] has a unique prime factorization, up to changing the order of the terms. | |
− | Prime factorizations are important in many ways, for instance, to | + | |
− | === | + | The form of a prime factorization is |
+ | <math>n = {p_1}^{e_1} \cdot {p_2}^{e_2}\cdot{p_3}^{e_3}\cdots{p_k}^{e_k}</math> | ||
+ | where <math>n</math> is any natural number, the <math>p_{i}</math> are prime numbers, and the <math>e_i</math> are their positive integral exponents. | ||
+ | |||
+ | Prime factorizations are important in many ways. One instance is to simplify [[fraction]]s. | ||
+ | |||
+ | ==Primes and Prime Factorization Video== | ||
+ | https://youtu.be/6xNkyDgIhEE?t=543 | ||
+ | |||
+ | ==Techniques== | ||
+ | |||
+ | The common method of prime factorization is checking prime numbers, case by case. Use [[divisibility rules]] to check if primes (or powers of primes) are a factor and then move up to a different prime if said prime is not a factor. When a prime is a factor, we factor out the prime and check for factors in the resulting number. | ||
+ | |||
+ | Sometimes, we could easily see that a number is a multiple of a composite number or a prime. For instance, <math>50</math> is a factor of <math>2650</math>, and <math>49</math> is a factor of <math>4998</math>. In these cases, a good strategy is to choose the number accordingly to make factoring easier. | ||
+ | |||
+ | ==Example== | ||
+ | |||
+ | Consider the number <math>38052</math>. | ||
+ | |||
+ | * Because the last two digits of the given number are a multiple of <math>4</math>, we can rewrite <math>38052</math> as <math>2^2 \cdot 9513</math>. Note that <math>9513</math> is not even, so we move on. | ||
+ | * Because the sum of digits of <math>9513</math> is a multiple of 9, we can rewrite <math>38052</math> as <math>2^2 \cdot 3^2 \cdot 1057</math>. Note that the sum of digits of <math>1057</math> is not a multiple of 3, so we move on. | ||
+ | * Because <math>1057</math> does not end in <math>0</math> or <math>5</math>, we skip <math>5</math> as a factor. As for <math>7</math>, after long division, we note that <math>1057 = 7 \cdot 151</math>, so we can rewrite <math>38052</math> as <math>2^2 \cdot 3^2 \cdot 7 \cdot 151</math>. However, when doing long division again, <math>151</math> is not a multiple of <math>7</math>, so we move on. | ||
+ | * Note that <math>11</math> is not a factor of <math>151</math>, so we can move on. In fact, because <math>13 > \sqrt{151}</math>, we can declare <math>151</math> as prime and stop. | ||
+ | |||
+ | Thus, the prime factorization of <math>38052</math> is <math>2^2 \cdot 3^2 \cdot 7 \cdot 151</math>. | ||
+ | |||
+ | ==Problems== | ||
+ | |||
+ | ===Introductory=== | ||
+ | * Practice Problems from [https://artofproblemsolving.com/alcumus/ Alcumus] | ||
+ | ** Prime Factorization (Prealgebra, Number Theory) | ||
+ | |||
+ | ===Intermediate=== | ||
+ | * [[2000 AIME I Problems/Problem 1]] | ||
+ | |||
+ | == Resources == | ||
+ | |||
+ | === Books === | ||
+ | * [http://www.artofproblemsolving.com/Books/AoPS_B_Item.php?page_id=10 Introduction to Number Theory] by [[Mathew Crawford]] | ||
+ | === Games === | ||
+ | * [http://thinkinghard.com/math/integers/PrimeShooter.html Prime Shooter] | ||
+ | |||
+ | |||
+ | ==See also== | ||
+ | *[[Divisor]] | ||
+ | *[[Divisibility rules]] | ||
+ | |||
+ | [[Category:Number theory]] |
Latest revision as of 22:14, 5 January 2024
For a positive integer , the prime factorization of
is an expression for
as a product of powers of prime numbers. An important theorem of number theory called the Fundamental Theorem of Arithmetic tells us that every positive integer has a unique prime factorization, up to changing the order of the terms.
The form of a prime factorization is
where
is any natural number, the
are prime numbers, and the
are their positive integral exponents.
Prime factorizations are important in many ways. One instance is to simplify fractions.
Contents
Primes and Prime Factorization Video
https://youtu.be/6xNkyDgIhEE?t=543
Techniques
The common method of prime factorization is checking prime numbers, case by case. Use divisibility rules to check if primes (or powers of primes) are a factor and then move up to a different prime if said prime is not a factor. When a prime is a factor, we factor out the prime and check for factors in the resulting number.
Sometimes, we could easily see that a number is a multiple of a composite number or a prime. For instance, is a factor of
, and
is a factor of
. In these cases, a good strategy is to choose the number accordingly to make factoring easier.
Example
Consider the number .
- Because the last two digits of the given number are a multiple of
, we can rewrite
as
. Note that
is not even, so we move on.
- Because the sum of digits of
is a multiple of 9, we can rewrite
as
. Note that the sum of digits of
is not a multiple of 3, so we move on.
- Because
does not end in
or
, we skip
as a factor. As for
, after long division, we note that
, so we can rewrite
as
. However, when doing long division again,
is not a multiple of
, so we move on.
- Note that
is not a factor of
, so we can move on. In fact, because
, we can declare
as prime and stop.
Thus, the prime factorization of is
.
Problems
Introductory
- Practice Problems from Alcumus
- Prime Factorization (Prealgebra, Number Theory)
Intermediate
Resources
Books
Games