{"name":"combinatorics","title":"Combinatorics Calculator (n!, nPr, nCr)","category":"math","description":"Factorial, permutations (nPr) and combinations (nCr) for non-negative integers.","price_usd":0.001,"input_schema":{"type":"object","properties":{"n":{"type":"integer","description":"Total number of items (non-negative integer)"},"r":{"type":"integer","description":"Number chosen (for permutations/combinations)"}},"additionalProperties":false,"required":["n"]}}