What does the fetch() function return?
I think you need something more like this:
$row = $stmt -> fetch();
echo( $row[ 'N1' ] );
Also, avoid using "select *" in Application code.
Whilst you might not have a lot of columns in that table [yet], databases are inherently shared entities and you never know when someone [else] might add a dozen columns full of gigabytes of stuff that this query simply doesn't care about. Always select just the columns that you specifically need.
Regards, Phill W.