便利帳– category –

【順列・組み合わせ】重複順列 (sequence with repetition)r人をn個の部屋に分ける$_{n}\Pi_{r}=\underbrace{n\times{n}\times\times{n}}_{r個の積}=n^r$順列の個数(permutation)$1\leqq x_1\ne x_2\ne\cdots \ne x_k \leqq n$$\displaystyle {}_n\mathrm{...