- 4

- 0

d = date of the month

m = number of the month in the year

y = year

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

afterwards, divide w by 7, and the remainder is the day of the week, according to:

1 - sunday

2 - monday

3 - tuesday

4 - wednesday

5 - thursday

6 - friday

0 - saturday

now, i totally understand the equation, and it works. but i just dont understand what the significance of the [y/4] [y/100] and [y/400] is.

why is it needed in the equation?