solving an equation $x^x= c$

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I would like to find a solution $x$ for $x^x = c$ where $c$ is a positive constant.

Firstly I'm looking for an approximative solution when $c$ tends to infinity.

Thank you in advance

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Use this formula $$ x = \frac{\log c}{W_k(\log c)}, k \in \mathbb{Z} $$ where $W_k$ is the $k$th branch of the product logarithm. This is the inverse of $f(x) = x^x$.