The A# on your EAD (OPT) card is not a real A#. Actually, you do

not have any A# until you file your immigration application and get an A# from the USCIS. You may use the "A#" on your EAD card when filing out the forms from your employer, but you should keep the related items in any forms to government as N/A. In fact, in most immigration application forms you can see the questions related to A# always end in "if any".