How programmatically send app to background

I don't think that it is possible. Unless there is a specific app that you want to start and put in front of your app.

You know. I have wrote app with two activities. Second one is transparent. From first activity user runs browser. Then program runs second activity in foreground mode. So user still sees browser through second trasparent activity. It's looks like a sandwich ( first activity of my app - browser - second activity of my app). .After some code runs second activity goes finished. But after this first activity comes in to foreground mode infront of browser. So this is a problem how to keep first activity still under browser in background mode after second activity is finished?
Thanks

How is the transparent activity started (when the browser is visible)?

It might be simpler to use a WebView instead of an external browser.

Yes transparent activity starting when browser is in foreground. I can't use WebView because my app must not use any Internet connections from it self. Browser is program - users choice. It can be any browser which was installed on device. Transparent activity starting after user press notification. In app I am using "Advance Notification" library. May be try to get info from system what browser user running and after transparent activity finished starting particular the same browser?

How are you showing the transparent activity when the browser if visible? Are you calling it from a service?

Well I call transparent activity from notification. I am using "advance notification" library. Probably it looks like a service, because notification still can calling second transparent activity when main activity is finished. You know I think I have found the answer for my question. I have made listing of all running apps on device in time when transparent activity is active. Then I get from list the app which is locating before mine. It's name I put in global verible of main activity. Then finished transparent activity. Android calls main activity resume sub. In resume sub a starting browser again if global veribls is not empty. To prevent of appiering of main activity before browser come up from pause mode I also making main activity transparent with no visible panels for a wile