Friday, the 13th

What a day… how often do we get Friday, 13th?

I tried looking online. To no avail. So I decided, maybe I could do a calculation myself. I’ll try.

There’s a mathematical formula to calculate the DAY of the week (Monday, Tuesday, Wednesday…), if you give me the DATE (13th Jan, 13th Feb, 13th Mar…)

Ok, you get the picture.

Let me try…

Ok, I’ll try to calculate backwards (day and date) instead of forwards.

First, the formula… I was surfing around and found this formula.

Here is a formula for finding the day of the week for ANY date.

N = d + 2m + [3(m+1)/5] + y + [y/4] - [y/100] + [y/400] + 2

where d is the number or the day of the month, m is the number of the month, and y is the year. The brackets around the divisions mean to drop the remainder and just use the integer part that you get.

Also, a VERY IMPORTANT RULE is the number to use for the months for January and February. The numbers of these months are 13 and 14 of the PREVIOUS YEAR. This means that to find the day of the week of New Year’s Day this year, 1/1/98 (or 2/2/98), you must use the date 13/1/97 (or 2+14/2/97).

Ok, I’m done. This is getting a lil too long… anyone help?