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0 votes
2 answers
494 views

Interesting ways to show that there are infinitely many equivalence relations on an infinite set (including Bell numbers).

I am trying to answer the question "Is there infinitely many equivalence relations on any infinite set?" My intuition says yes, and when I try to prove this, I feel like my reasoning is not ...
Natasha's user avatar
  • 131
1 vote
1 answer
55 views

Alternative representation for $B_{n,k}(1!,\dots,(n-k+1)!)$

Let $B_{n,k}$ be the Exponential Bell Polynomial and $\hat {B}_{n,k}$ the Ordinary Bell Polynomial. One has the identity: $$ B_{n,k}(0!,1!,\dots,(n-k)!) = |s(n,k)|, $$ with $s(n,k)$ the Stirling ...
HolyMonk's user avatar
  • 1,135
3 votes
1 answer
256 views

What's the sum of the series $\sum\limits_{n\geq 0}\frac{n^x}{n!}$ with $x$ a positive real number?

By the ratio test the series $$ \sum_{n\ge0}\frac{n^x}{n!} $$ is convergent, but I know no method to evaluate it. Since it's a convergent series then my question here is: Is there a closed form ...
zeraoulia rafik's user avatar