Php Alpha numeric genrator code

Hey I am facing in genarating randomly the specific code in format it is given.I want to produce code of same way as x55769w0ecb4f9k3 .Should get numbers in numbers place and aplhabet in their place.I am programming in php.I need to generate a thes two codes(one above and

same way this code too APA91bF4ETz2QhQZ8JcbB6TQHPdYa6v7TBnEIrjRySftQrjCVuvYs7owqqTgS76cHN6xmGzzA_rkRuOYuXIo5Po0ngOqo0h_NyAORa899WAwmSgiALdXsjo