Articleship certificate number?

Friends..

Can someone please help me. I'm trying to fill the application form online - PCE Nov 2012.

There's a column which says "Articleship certificate number" 
can someone please tell me what exactly it is..

I've verified the letter I got from ICAI after I submitted my form 108. 
There's no such thing as "Articleship certificate number" in there..

please help.

Regards, 
Divya