10. =WEEKNUM (A2,2) Number of the week in the year that 3/9/2012 occurs, based on a week beginning on Monday (the second argument, 2). 11. Returns the week number of a specific date. For example, the week containing January 1 is the first week of the year, and is numbered week 1. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.