Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

permutation

A bijection from a finite set to itself -- a rearrangement of the set's elements.

Loading interactive…

Examples

The permutation of $\{1,2,3,4\}$ sending $1\to2,\ 2\to1,\ 3\to4,\ 4\to3$ .