Explain Your Username

[mjk45]

My user name mjk45 , is made up of my initials and the addition of 45 came about later ,I found out the ISP my mum was on had a small gaming site so I joined using just my initials for my user name, not long after (this was a long time ago) the network moved from ADSL to Broadband and we had to redo our usernames but when i went to redo mine it told me it was taken so I added the number 1 at the end only to get the same answer after doing this up to around 8 with the same result I randomly chose 45 and that was accepted . it turned out that my original username wasn't taken at all but they had made the letter/number combination a minimum of 5 but failed to notify us