How do you get Jacobi symbol $[\frac{3}{8}]$?

How do you get $[\frac{3}{8}]$? Answer is -1, but how do you get that?

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I thought Jacobi symbol $\left(\frac an\right)$ is defined only for odd $n$. –  Martin Sleziak Dec 3 '11 at 10:50
That's true but when you input "Jacobi symbol(3,8)" in the wolframalpha.com/input/?i=Jacobi+symbol%283%2C8%29 you get -1. Might be false. –  alvoutila Dec 3 '11 at 10:52
Maybe that's supposed to be a Kronecker symbol instead of a Jacobi symbol... –  Guess who it is. Dec 3 '11 at 10:55
@alvoutila: Mathematica actually generalizes JacobiSymbol[] to effectively act like KroneckerSymbol[]. –  Guess who it is. Dec 3 '11 at 10:56
Dear @Martin: +1 for your comment, and thanks for all your editing work!!! –  Pierre-Yves Gaillard Dec 3 '11 at 11:00