# Tell Wolfram Alpha that a variable is a natural number

how can I tell Wolfram Alpha that some variables are natural numbers, when I want to solve a equation?

Cheers

What I want to do:

$\binom{n}{k}\cdot p^k \cdot (1-p)^{n-k} = \frac{1}{\sqrt{n\cdot p \cdot (1-p)}}\cdot \frac{1}{\sqrt{2 \cdot \pi}} \cdot e^{-\frac{1}{2} \cdot \left(\frac{x-np}{\sqrt{n \cdot p \cdot (1-p)}}\right)^2}$ solve for $x$ with $n,k \in \mathbb{N}$, $0 \lt p \lt 1$.

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Do you have an example? –  Amzoti Oct 31 '13 at 17:05

Just add an "assuming x integer" at the end. I tested it, and it seems to work. (similar to Maple's notation assuming x::integer, I guess) For natural it doesn't seem to work properly: assuming x natural

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Solve[(x - 3/2) (x - 2)== 0 && x $\in$ Integers]