Prime numbers are fundamental in Number Theory as they cannot be expressed as a product of two smaller natural numbers, making them the basic units from which all other natural numbers are constructed.

Pythagoras, a renowned Greek philosopher and mathematician, is often credited as the father of Number Theory for his contributions to the study of prime numbers and the Pythagorean theorem.

Fermat's Last Theorem, famously proven by Andrew Wiles in 1994, asserts that there are no three positive integers a, b, and c that can satisfy the equation a^n + b^n = c^n for any integer n greater than 2.

Modular arithmetic, a branch of Number Theory, involves working with integers modulo a fixed positive integer, and it is primarily used to solve Diophantine equations, which are polynomial equations with integer coefficients.

The Riemann Hypothesis, proposed by Bernhard Riemann in 1859, is one of the most significant unsolved problems in mathematics. It concerns the distribution of prime numbers and has profound implications for various areas of mathematics, including Number Theory.

The fundamental theorem of arithmetic states that every integer greater than 1 can be expressed as a unique product of prime numbers, up to the order of the factors.

The ring of integers, denoted by ℤ, is a mathematical object consisting of all integers, along with the operations of addition and multiplication. It is used to study the properties of integers and their relationships.

The Goldbach conjecture, proposed by Christian Goldbach in 1742, states that every even integer greater than 2 can be expressed as the sum of two prime numbers. It remains unproven, despite extensive efforts by mathematicians.

The prime number theorem, a fundamental result in Number Theory, provides an approximation for the number of prime numbers less than a given number. It has significant implications for the study of the distribution of prime numbers.

Diophantine equations, named after the Greek mathematician Diophantus, are polynomial equations with integer coefficients. They are used to solve real-world problems involving integers, such as finding integer solutions to linear equations or determining the number of ways to represent a given number as a sum of squares.

The modular group, denoted by SL(2, ℤ), is a mathematical object consisting of all 2x2 matrices with integer entries and determinant 1. It is used to study the properties of modular arithmetic and has applications in various areas of mathematics, including Number Theory.

Number Theory plays a crucial role in cryptography, the science of secure communication. Many cryptographic algorithms, such as RSA and elliptic curve cryptography, rely on the properties of prime numbers and other concepts from Number Theory to ensure the security of data transmission.

Euler's totient function, denoted by φ(n), is a mathematical function that counts the number of positive integers less than or equal to n that are relatively prime to n. It is used to study the relationship between prime numbers and perfect numbers, which are positive integers that are equal to the sum of their proper divisors.

Perfect numbers, positive integers that are equal to the sum of their proper divisors, are significant in Number Theory. They are used to study the properties of prime numbers and have been a subject of mathematical investigation since ancient times.

Mersenne primes, prime numbers of the form 2^p - 1 where p is a prime number, are significant in Number Theory. They are used to study the relationship between prime numbers and perfect numbers, and have applications in various areas of mathematics, including cryptography.