Is it possible to see the sourcecode of the app?

Hello

I like the technical features of this app on Google's Play store:
"Easter Sunday Calculator" (i'm not allowed to post links yet)

Is it possible to make them visible by downloading it?
Or can someone give me the technical keywords on how this app was programmed?
I want to make something similar, preferably with the MIT App Inventor 2.

Thanks!
Emiel