Is there an app for iphone that can notify me whenever my mac powers on?
You could certainly script this. There are many approaches that would work. It depends on how comfortable you are with the various tools, and if your Mac automatically logs into a user account.

If your Mac automatically logs into your account on powering on, consider using Automator or AppleScript, and Twitter.

Automator and Twitter

Consider combining this article on Automator and Twitter. You could send a private tweet when your account is logged in. Save the workflow as an application and add it your account's Login Items: System Preferences > Users &amp; Groups

Alternative Approaches

If your Mac does not automatically log into a user account, you will need to use a shell script approach. Automator and AppleScript both require an active user session.

You could use AppleScript or shell script for sending a messages or e-mail. Add launchd or a third party tool for scheduling the event on start-up or login.

This can all be integrated into IFTTT as a trigger.