Pathway XIX·b

CCombinatorics

Counting without listing. Binomial coefficients are the cells of Pascal's triangle.

1. 01Binomial coefficientsC(n,k) counts k-subsets of an n-set. Pascal's identity is a lattice path split.4 min
2. 02PermutationsAn n-permutation is a bijection on n letters. There are n! of them; cycles write the rest.4 min