How do you query large MySQL table for entries that don't start with an ASCII letter?

Question

Is there a performant way to query a large MySQL table for all entries that don't start with a letter?

I get the correct results using this, but it cannot take advantage of indexes:

SELECT * FROM `companies` WHERE `name` NOT REGEXP '^[a-z]+'

Edit: Anything better than the following?

SELECT * FROM `companies` WHERE `id` NOT IN (SELECT `id` FROM `companies` WHERE `name` RLIKE '^[a-z]');