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Tonelli-Shanks Algorithm (by Example)

Okay, so you understand how to check if a quadratic congruence is solvable, but how do you find the solutions? In this article, I cover the Tonelli-Shanks algorithm by working through several examples. I also give a complete solution to a general quadratic congruence equation.

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Euler’s Totient Function and Euler’s Theorem

Many people have celebrated Euler’s Theorem, but its proof is much less traveled. In this article, I discuss many properties of Euler’s Totient function and reduced residue systems. As a result, the proof of Euler’s Theorem is more accessible. I also work through several examples of using Euler’s Theorem.

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Fermat’s Theorem (and Wilson’s Theorem)

Maybe you have heard of Wilson’s Theorem? But did you know that’s is converse also holds. In this article, I prove both Wilson’s Theorem, its converse, and Fermat’s Theorem. Then you will also see many examples using Fermat’s theorem.

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Chinese Remainder Theorem (The Definitive Guide)

This definitive guide covers proofs, examples, algorithms, applications, and the Chinese Remainder Theorem history. It also includes links to additional resources such as online articles, courses, books, and tutors to help students learn from various sources. Professionals can also use these resources to increase their knowledge of the field or help structure courses for their students.

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Applications of Congruence (in Number Theory)

So you probably know a divisibility test for 2, 3, and 5. But what about 7, 11, 13, or even larger primes? In this article, I go over divisibility tests. Including how to create your own. I also discuss the Days of the Week problem, where you are to determine the day of the week from a given date very quickly.

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Polynomial Congruences with Hensel’s Lifting Theorem

The idea behind solving polynomial congruence equations is that we can reduce a congruence equation to an equivalent system of congruence equations using prime factorization. We then 1) solve each equation modulo a prime number (by brute force), 2) use Hensel’s Lifting theorem, and then 3) piece together the solutions using the Chinese Remainder Theorem. We provide several nontrivial examples many of which are workable by hand.

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Linear Congruences and Their Solvability

In this article, you will learn what linear congruences are and when they are solvable. How to solve them will also be covered in detail. I discuss an ad hoc method, using the Euclidean algorithm, and using the inverse of an integer.

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Congruence Theorems (and Their Proofs)

In this article, I discuss modular congruence. I demonstrate the congruence is an equivalence relation, and I prove several lemmas concerning the basic properties of congruence. Towards the end, I go over modular arithmetic and its properties.

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Diophantine Equations (of the Linear Kind)

In this article, I discuss what Diophantine Equations are and the difficulting of solving them. Then, I detail how to solve two-variable linear diophantine equations. Towards the end, I solve a multi-variable linear Diophantine equation concerning pennies, dimes, and quarters.