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Let $S=\{m\cdot n^r\mid m,n\in\mathbb Z,r\in\mathbb Q\}$
Can $e$ or $\pi$ be written as a finite sum of elements of $S$?

Can $\pi=xe$, with $x$ algebraic?

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    See also [this thread](http://mathoverflow.net/questions/40145).2011-11-27

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As finite sums, no. If you could, you'll get that $\pi$ and $e$ are algebraic numbers, which is known to be false.

As infinite sums:

$e = \sum_{n=0}^{\infty} \frac1{n!}$

$\pi = 4\sum_{n=0}^{\infty} \frac{(-1)^n}{2n+1}$