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Excel

The WEEKNUM function in Excel takes a date and returns the number of the week starting from 1. The function takes into account the week number and the day of the week that the date falls on. The function can be used to calculate the week number for a given date, or to return the date for a given week number.

The syntax of WEEKNUM in Excel is as follows:

=WEEKNUM(serial_number)

Where "serial_number" is the serial number of the date you want to find the week number for.

To use WEEKNUM in Excel, you would first enter the formula =WEEKNUM(serial_number) into a cell, where "serial_number" is the serial number of the date you are using. WEEKNUM will then return the week number for that date. An example of how to use WEEKNUM in Excel would be to find the week number for the date January 1, 2016. To do this, you would enter the formula =WEEKNUM("1/1/2016") into a cell, and WEEKNUM would return the week number for that date, which would be week 1.

There are a few occasions when you should not use WEEKNUM in Excel. One is when you are trying to calculate the week number for a date that is outside of the range of dates for which WEEKNUM returns a valid result. For example, if you try to use WEEKNUM to calculate the week number for January 1, 2019, it will return a result of 1, even though the correct week number for that date is 52.

Another occasion when you should not use WEEKNUM is when you are working with a table that has been sorted in a non-standard way. For example, if you have a table that is sorted in reverse chronological order, with the most recent dates at the top, WEEKNUM will return the wrong result for any dates that are located at the bottom of the table.

The Excel WEEKNUM function returns the number of the week in the year for the date given as the argument. The first week of the year is the week that contains January 1st, and the last week of the year is the week that contains December 31st. Here are a few other formulae that you can use to calculate week numbers in Excel:

=WEEKDAY(DATE(YEAR(A1),1,1))

-1 This formula returns the week number for the date in A1. The week number is calculated by subtracting 1 from the weekday number for the date.

=INT(WEEKNUM(DATE(YEAR(A1),1,1))) This formula returns the week number for the date in A1 as an integer.

=MOD(WEEKNUM(DATE(YEAR(A1),1,1)),7) This formula returns the week number for the date in A1 as a decimal number. The week number is calculated by dividing the week number by 7 and rounding the result to the nearest integer.

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