# Combinatorics Calculator

A skill for combinatorial calculations.

## Overview

This skill provides implementations for combinatorial calculations with proper modular arithmetic handling for competitive programming.

## Key Features

- Factorial precomputation
- Combinations and permutations
- Special number sequences
- Lucas theorem support
- Inclusion-exclusion helper

## Combinatorial Functions

### Basic
- Factorial
- Combinations (nCr)
- Permutations (nPr)

### Special Numbers
- Catalan numbers
- Stirling numbers
- Bell numbers
- Derangements

## Related Skills

- SK-ALGO-021: number-theory-toolkit
- SK-ALGO-022: prime-sieve-generator
- AG-ALGO-018: number-theory-specialist
