A finishing carpenter friend of mine recommended I try to use Pythagoras’ Theorem when I asked him, out of desperation, for advice on a difficult math problem that I am stuck on.

When I reported no progress, he asked what other topics in math are named after people, after all, Pythagoras lived a long time ago.

So here’s a very simple list (for now not even in a good order). Please use the links to learn more about what is being named.

• Algorithm, denoting a method of calculation, is named after Abū ʿAbdallāh Muḥammad ibn Mūsā al-Khwārizmī (Algorithm being his name in Latin). Basic example is the Euclidean algorithm, to calculate the greatest common divisor (of two or more numbers).
• Fibonacci numbers, or Fibonacci sequence, named after Leonardo Pisano Bigollo, also called Leonardo Fibonacci. Each number in the sequence is the sum of the previous two numbers, starting with 0 and 1. This sequence begins 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, …
• The Euler number, the base of the natural logarithms, is named after Leonard Euler.  Often just “e”: 2.71828… Much more in the world of math is named Euler.
• Cartesian coordinate system, named after René Descartes. The grid with axes, usually called x and y.
• The Bernoulli numbers, are named after Jakob Bernoulli. They appear in series expansions of trigonometric functions.
• Fermat’s theorem, named after Pierre de Fermat. A method for finding maxima and minima of functions.
• Pascal’s triangle, named after Blaise Pascal. The triangle arranges the binomial coefficients.
• Taylor series are named after Brook Taylor. These series represent mathematical functions as infinite sums of simple terms.
• Newton’s method, also, called Newton–Raphson method, named after Isaac Newton, and Joseph Raphson. Method to approximate a zero of a function.
• Galois theory, named after Évariste Galois. Allows proving such things as why there is no formula for the roots of a fifth degree polynomial equation, or why it is not possible to trisect all angles using a compass and straightedge.
• The Lagrangian, named after Joseph Lagrange. Functions that describe how dynamical systems change over time. More in maths is named Lagrange
• Dirichlet’s principle, named after Johann Dirichlet. If you have more items than containers, and distribute all items among the containers, then one container will have more than one item.
• Gaussian elimination, named after Card Friedrich Gauss. An algoritm (see above) for solving systems of linear equations.
• Hamiltonian path, named after William Hamilton. A path in a graph that visits each vertex exactly once.
• Riemann sum, named after Bernhard Riemann. Method for approximating areas given by a curve. Much more in math is named Riemann.
• Hilbert’s Nullstellensatz, named after David Hilbert. Connecting algebra and geometry.
• Turing machines, named after Alan M. Turing. A simple reference model for computation.

There are many, many more, especially from the last century. For example, I left out the Tutte Graph. Wikipedia has a list of things named after mathematicians, however it is still far from complete.

To finish, I’ll list one of a different kind: the Erdős number is the distance to Paul Erdős in terms of coauthorship. (My Erdős number presently is 4)