I agree with others here that you shouldn't autogenerate usernames from names if you can help it. FYI, we have auto-generated usernames in the university computer lab of the form js429 where "js" is the initials of the person always coerced to [a-z]{2}, and "429" is a three-digit number somehow generated from the name and other user data.¹ There are 14200 such usernames. (The most common initials are sa(280), ka(244), ba(206), sg(191), kg(180), kz(149), bg(140).)