## anonymous one year ago Let A and B be nonempty ﬁnite sets with |A| = m and |B| = n If m > n, then ﬁnd the number of onto functions from A to B

1. misty1212

HI!!

2. misty1212

you need the formula or an explanation?

3. misty1212

if you just need the formula it is $\sum_{k=0}^n(-1)^k\binom{n} {k}(n-k)^m$

4. misty1212

if you need an explanation, here is a decent one http://math.stackexchange.com/questions/334420/number-of-onto-functions