Improper integral of $x^{-x}$

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Is the following improper integral known? $$\int_{0}^{\infty} x^{-x} \, dx$$ Wolfram Alpha gives both the proper integral from 0 to 10 and 0 to 10000 as 1.99546 so I'm assuming it's equal to 2 (though it could actually be 1.99546), but is this known?