What are the prerequisites for the development of Android applications?

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C#

Mobile

Android

C#4.0

hi
i'm intermediate in c# .

i want develop android application using c#

what is easest way for do it ?

if possible , i want a free software that link with c#

please tell me about basic prerequisites ...

for example tell me : "YOU MUST FIRST LEARN XMLA AND WORK WITH ECLIPSE"

thanks my friends