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May 17 edit

Hyper-Exponential Function edit

f(x)={\frac {1}{e}}\cdot \sum _{n=0}^{\infty }{n^{x} \over n!}

1. Why does this function return positive integer values for all positive integer arguments ?

Obviously, this is related to the fact that

e=\sum _{n=0}^{\infty }{1 \over n!}

... just not sure how exactly ...

f(n)\in \mathbb {N} ^{*}\ ,\forall \ n\in \mathbb {N} ^{*}

— Proof here

2. Are there any simpler methods of computing these positive integer values, either directly or recursively ?

n	1	2	3	4	5	6	7	8	...
f(n)	1	2	5	15	52	203	877	4140	...

— Have you seen A000110, which gives hundreds of ways of computing these numbers?

70.162.4.242 (talk) 08:04, 17 May 2013 (UTC)[reply]

— See also

79.113.240.146 (talk) 15:00, 19 May 2013 (UTC)[reply]

3. Does this function have any special meaning or interesting properties ?

e^{e^{x}}

.

79.113.212.91 (talk) 07:52, 17 May 2013 (UTC)[reply]

— They're called Bell numbers and that formula above is Dobinski's formula.

Dmcq (talk) 12:32, 17 May 2013 (UTC)[reply]

Resolved