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Number Theory Basics
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Fundamental Theorem of Arithmetic
Every integer greater than 1 can be uniquely factorized into prime numbers. This theorem ensures that we can break down any number into a product of its prime factors in only one way, excluding the rearrangement of the prime factors.
Pythagorean Triple
A Pythagorean triple consists of three positive integers , , and , such that . These are the integer solutions to the Pythagorean theorem for right triangles.
Legendre's Conjecture
Legendre's Conjecture suggests that there is at least one prime number between any two consecutive squares and . This conjecture has not been proven or disproven.
Lagrange's Four-Square Theorem
The theorem states that every natural number can be represented as the sum of four integer squares. That is, for every , there exist integers such that .
Euler's Criterion
Euler's Criterion is a statement in number theory that gives a condition for determining whether an integer is a quadratic residue modulo a prime. For an integer and an odd prime , is a quadratic residue modulo if and only if .
Euler's Theorem
Euler's Theorem is a generalization of Fermat's Little Theorem. It states that if is a positive integer and is an integer coprime to , then where is Euler's totient function.
Dirichlet's Theorem on Arithmetic Progressions
The theorem states that for any given two positive coprime integers and , there are infinitely many primes of the form , where is a non-negative integer. This result shows that there are numerous numbers with the same difference between them that are prime.
Carmichael's Theorem
Carmichael's Theorem is a result in number theory that generalizes Fermat's little theorem. It states that for Carmichael numbers , for all integers that are coprime to , it holds that .
The Density of Primes
The Density of Primes, given by the Prime Number Theorem, approximates the distribution of the primes by stating that the probability of a number around being prime is about , where is the natural logarithm.
Euclid's Lemma
If a prime divides the product of two integers and , then must divide at least one of those integers or . This is fundamental in the study of number theory because it leads to the unique factorization of integers.
Fermat's Little Theorem
If is a prime number, then for any integer , the number is an integer multiple of . In the notation of modular arithmetic, this is expressed as .
Bezout's Identity
Bezout's Identity states that for any non-zero integers and , there exist integers and such that , where denotes the greatest common divisor of and .
The Goldbach Conjecture
The Goldbach Conjecture is one of the oldest and best-known unsolved problems in number theory and all of mathematics. It states that every even integer greater than 2 is the sum of two prime numbers.
Gauss's Lemma
In number theory, Gauss's Lemma relates to the Legendre symbol and gives a way to compute it. For a given odd prime and an integer not divisible by , the Legendre symbol is equal to where is the number of integers such that .
Möbius Function
The Möbius function is a multiplicative function that is used in number theory and combinatorics. It is defined for a positive integer such that:
The Pell Equation
The Pell Equation is a diophantine equation of the form where is a non-square natural number. The solutions are called Pell numbers. This equation is central to the theory of quadratic forms and has an infinite number of solutions.
The Partition Function
In number theory, the Partition Function represents the number of distinct ways of representing as the sum of positive integers, without considering the order of addends. For example, because 4 can be partitioned as 4, 3+1, 2+2, 2+1+1, and 1+1+1+1.
Fermat's Last Theorem
Fermat's Last Theorem states that there are no three positive integers and such that for any integer value of greater than 2. This was famously conjectured by Pierre de Fermat in 1637 and was only proven in 1994 by Andrew Wiles.
Wilson's Theorem
An integer is a prime number if and only if is divisible by where denotes the factorial operation. In modular arithmetic, this can be written as .
Euler's Totient Function
Euler's Totient Function counts the number of positive integers less than or equal to that are coprime to . It is a key function in number theory, particularly in modular arithmetic and theorems involving congruences.
The Division Algorithm
Given two integers and , with , there exists unique integers and such that and . The number is called the quotient, while is the remainder.
The Quadratic Reciprocity Law
This is a theorem in number theory that allows the determination of the solvability of quadratic equations modulo prime numbers. It provides a relationship between the Legendre symbols and for any two odd primes and .
Sophie Germain Prime
A Sophie Germain prime is a prime number such that is also prime. The number is called a safe prime. These primes are named after French mathematician Sophie Germain, who used them in her work on Fermat's Last Theorem for the case .
The Mersenne Prime
A Mersenne prime is a prime number of the form for some integer . Not all numbers of this form are prime, but primes of this form are used in large number cryptography.
The Twin Prime Conjecture
The Twin Prime Conjecture asserts that there are infinitely many pairs of prime numbers (p, p+2) such that both numbers are prime. A pair of primes is called a 'twin prime'.
The Riemann Hypothesis
The Riemann Hypothesis is a conjecture that the nontrivial zeroes of the Riemann zeta function all have real part 1/2. This hypothesis has profound implications on the distribution of prime numbers.
Pigeonhole Principle
The Pigeonhole Principle states that if items are put into containers, with , then at least one container must contain more than one item. This simple yet powerful principle is used in various mathematical proofs.
Chinese Remainder Theorem
If one knows the remainders of the division of an integer by several pairwise coprime integers, then one can determine uniquely the remainder of the division of by the product of these integers, up to the product of these integers.
Ramsey's Theorem
Ramsey's Theorem states that for any given positive integers and , there is a minimum number such that if the edges of a complete graph of at least vertices are colored with two colors, there is a monochromatic -subset or a monochromatic -subset. This theorem is a fundamental result in combinatorial number theory and graph theory.
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