Combinatorics

Fundamentals
    Finding Power of Factorial Divisor
    Binomial Coefficients
    Catalan Numbers
Techniques
    The Inclusion-Exclusion Principle
    Burnside's lemma / Pólya enumeration theorem
    Stars and bars
    Generating all K-combinations
Tasks
    Placing Bishops on a Chessboard
    Balanced bracket sequences
    Counting labeled graphs