Please URGENT subscript help! (On google chrome)

I googled around and found that the way to input subscripts is CTRL+ -

The problem is google chromes zoom out hotkey is CTRL + - and it cannot be disabled, therefore I cannot input subscripts in wolfram alpha..pretty ridiculous. How do I work around this please? Its very urgent.

Im trying to calculate simple problems like this Imgur: The magic of the Internet

You could do a[n]=... and maybe that will have the same interpretation?