Interactive pages for Combinatorics

Subsets
Ordered and unordered combinations
The National Lottery
The binomial expansion
Pascal's triangle
Pascal's identity
Complements
Grid routes
Counting solutions to some equations
An extension of Pascal's identity
Sum of numbers in a triangle
Counting subtriangles
Lines across circles
Covering a chess board with dominos
Tetris
The seven bridges of Königsberg
Numbers of hairs
Handshaking
Sums of subsets
Modular sums
Piggy bank
Tennis and squash
Tennis, squash and badminton
Derangements of 1234
Derangements of 12345
Numbers coprime with 42
Matching problems

Basic rook problems	, ,
Rooks and permutations
Rook polynomial for the full board
Rooks and derangements
Snap
Problème des ménages
Blocking and stripping
Factoring rook polynomials
Extending a latin rectangle
Solving the Problème des ménages
Solving the Snap problem with Python
Counting the sets $S_X$
Staircase
The Rugby World Cup
A consistent tournament
Odd modular tournament
World Super-Dodgy Wrestling League
Medals
The medal ceremony allocation problem
A big Latin square
Latin square for the dihedral group $D_8$
Latin square for addition mod $10$
Extending another latin rectangle
Orthogonal latin squares
Reduced latin squares of size $4$
Affine plane design over $\mathbb{Z}/3$
Quadratic residue design over $\mathbb{Z}/7$