2: Prime Numbers
Prime numbers, the building blocks of integers, have been studied extensively over the centuries. Being able to present an integer uniquely as product of primes is the main reason behind the whole theory of numbers and behind the interesting results in this theory. Many interesting theorems, applications and conjectures have been formulated based on the properties of prime numbers. In this chapter, we present methods to determine whether a number is prime or composite using an ancient Greek method invented by Eratosthenes. We also show that there are infinitely many prime numbers. We then proceed to show that every integer can be written uniquely as a product of primes. We introduce as well the concept of diophantine equations where integer solutions from given equations are determined using the greatest common divisor. We then mention the Prime Number theorem without giving a proof of course in addition to other conjectures and major results related to prime numbers.
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- 2.3: The Fundamental Theorem of Arithmetic
- The Fundamental Theorem of Arithmetic is one of the most important results in this chapter. It simply says that every positive integer can be written uniquely as a product of primes. The unique factorization is needed to establish much of what comes later. There are systems where unique factorization fails to hold. Many of these examples come from algebraic number theory. We can actually list an easy example where unique factorization fails.
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- 2.5: Linear Diophantine Equations
- In this section, we discuss equations in two variables called diophantine equations. These kinds of equations require integer solutions. The goal of this section is to present the set of points that determine the solution to this kind of equations. Geometrically speaking, the diophantine equation represent the equation of a straight line. We need to find the points whose coordinates are integers and through which the straight line passes.
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- 2.7: Theorems and Conjectures involving prime numbers
- We have proved that there are infinitely many primes. We have also proved that there are arbitrary large gaps between primes. The question that arises naturally here is the following: Can we estimate how many primes are there less than a given number? The theorem that answers this question is the prime number theorem.
Contributors and Attributions
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Dr. Wissam Raji, Ph.D., of the American University in Beirut. His work was selected by the Saylor Foundation’s Open Textbook Challenge for public release under a Creative Commons Attribution ( CC BY ) license.