If the number is present there always, you can use this to "remove the first word":
CODE
$substr(%artist%,$strchr(%artist%,' ')+1,$len(%artist%))
If you want it to work only when the tag begins with a (positive) number:
CODE
$ifgreater(%artist%,0,$substr(%artist%,$strchr(%artist%,' ')+1,$len(%artist%)),%artist%)
Now do yourself a favor, click the "Title Formatting Help" entry in the main menu and try to understand what the above code really does.