Explaining, convincing and proving

Yatir from Israel describes his method for summing a series of triangle numbers.

We continue the discussion given in Euclid's Algorithm I, and here we shall discover when an equation of the form ax+by=c has no solutions, and when it has infinitely many solutions.

A introduction to how patterns can be deceiving, and what is and is not a proof.

An introduction to some beautiful results in Number Theory.