Why don't astronomers use everyday units to measure distances (what is an AU or a pc)? (Intermediate)
How this formula works: The WEEKNUM function takes two arguments, a date, and, optionally, an argument called return_type, which controls the scheme used to calculate the week number. See the WEEKNUM page for more information. B4 contains a date value for January 5, 2016. The DAY function returns the number 2 representing the calculated week number. Note that by default, the WEEKNUM function uses a scheme where week 1 begins on January 1, and week 2 begins on the next Sunday (when the return_type argument is omitted, or supplied as 1).
A bit late to the party, but this also works if you have the week number. For example, if you have week number 23, you can determine the month with the following modification to the formula: =TEXT(A1*7,mmm). Follow the same logic presented in the above table, just swap the numbers as needed.