How to find someone's register number without asking them....

Anna University Chennai register no. format 
1st 4 digits-college code Eg:7138 for Sri Ramakrishna Institute of Technology
2nd 2 digits-year Eg:11 for year 2011,12 for year 2012 ie year of joining
3rd 3 digits-course code Eg:105 for EEE
4th 3 digits-roll no, Eg:057
Eg:713811105057.
Download college codes here
COLLEGE CODES 
Course codes
101-Aeronautical
102-Automobile
103-CIVIL
104-CSE
105-EEE
106-ECE
114-Mech
205-IT