Conditional for author

I am trying to add some conditional text for a specific post author. Normally the byline for an author says ‘By [author name]’. For one particular author I want it to read ‘Posted by [author name]’. I have tried the following on the archive template but with no success:
<?php if (author_name('3')) { ?>Posted <?php } ?>by <?php the_author() ?>

Any suggestions on how to do this?