Generate of year and week numbers

I'm trying to create serial number who combine:

1) Last two digits in year: Year 2013 should be generated as 13.

2) Two digit for week number regarding to current date of creation: 20th - 26th of January 2014 is 04 (week 4 of the year).

3) Six digits start from 000001

My question is: How can I generate the year and week number? These numbers are always combined with "Today" so you don't have the option to manual set dates.