# What is Number Theory Number theory, part of mathematics focused on properties of the good integers (1, 2, 3, �). Occasionally referred to as higher arithmetic, it is among the oldest and a lot natural of mathematical pursuits. Number theory has usually fascinated amateurs along with professional mathematicians. As opposed to other divisions of mathematics, many of the issues and theorems of number theory could be understood through laypersons, even though solutions to the problems and proofs of the theorems usually require a sophisticated mathematical history.

Until the mid-20th century, number theory had been considered the purest department of mathematics, without direct applications to the actual world. The advent of digital communications and digital computers uncovered that number theory might provide unexpected answers to real-world issues. At the same time, improvements within computer technology allowed number theorists to make outstanding advances in determining primes, factoring large numbers, solving numerical problems and testing conjectures once regarded out of reach.

## Elementary Number Theory

Elementary number theory entails divisibility between integers the division algorithm, the Euclidean algorithm (and therefore the existence of finest common divisors), elementary properties of primes (the infinitude of primes, the special factorization theorem), congruences (and the structure from the sets  Z/nZ  as commutative rings), such as Euler's theorem extending it and Fermat's little theorem. However the term "elementary" is generally used in this setting simply to mean that no advanced equipment from other areas are employed not that the outcomes themselves are easy.

Indeed, a course in elementary number theory usually contains elegant and classic outcomes such as Quadratic Reciprocity; counting results utilizing the Mobius Inversion Formula (and other multiplicative number-theoretic functions) and also the Prime Number Theorem, asserting the approximate density of primes between the integers, which has hard but elementary proofs.

Other subjects in elementary number theory the options of sets of linear congruence equations (the Chinese Remainder Theorem) or solutions of individual binary quadratic equations (continued fractions and Pell's equations) or the generation of Pythagorean triples or Fibonacci numbers turn out in retrospect being harbingers of sophisticated equipment and themes in other locations.

## Algebraic Number Theory

Algebraic number theory is a significant branch of number theory that studies algebraic structures linked to algebraic integers. This is normally accomplished through considering a ring of algebraic integers O within an algebraic number area K/Q and learning their algebraic properties including the behaviour of ideals, factorization and field extensions. In this setting, the common features of the integers for example unique factorization need not hold. The virtue of the main machinery used group cohomology, Galois theory, group representations and L-functions is that it permits one to cope with new phenomena and yet partially recover the behaviour of the most common integers.

One of the very first properties of Z that can easily fail in the ring of integers O of an algebraic number area K is that of the special factorization of integers in to prime numbers. The prime numbers in Z tend to be generalized to irreducible components in O and though the unique factorization of factors of O into irreducible components may hold in some instances (such as for that Gaussian integers Z[i]), it may also fail, as in the situation of Z.

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