Divisible 400 facts

While investigating facts about Divisible 400, I found out little known, but curios details like:

Despite being divisible by 4, the year 2100 won't be a leap year, this happens every century if the year is not divisible by 400

The leap year occurs whenever the year is divisible by 4. This is not applicable if the year is divisible by 100, UNLESS it is also divisible by 400.

In my opinion, it is useful to put together a list of the most interesting details from trusted sources that I've come across. Here are 21 of the best facts about Divisible 400 I managed to collect.

1. Each century skips a leap year if not divisible by 400.

2. Leap years don't actually happen every four years. Leap days are added in years divisible by four, unless the year is also divisible by 100. If the year is also divisible by 400, a leap day is added regardless. So 1900, not a leap year.

3. A leap year isn't actually every 4 years. In the event that the year is divisible by 4 and 100, it is not a leap year, unless it is also divisible by 400.

4. A century year cannot be a leap year unless it is divisible by 400. Thus 1700, 1800, and 1900 were not leap years, but 1600, 2000, and 2400 are leap years

5. By the rules of the Gregorian Calendar, any centurial year (ends in 00) skips the leap day - that is, unless the year is divisible by 400.

6. The 33rd Waffen Grenadier Division of the SS Charlemagne (1st French) had a strength of between 7,400 to 11,000 men in 1944. In may 1945 only 60 men remained.

7. Not every fourth year is a leap year. This does not hold true on leap years that would fall in a year divisible by 100 (aka 2100) with the exception that leap years will be held on years divisible by 400.

8. Leap years occur on years divisible by 4 but never on years divisible by 100 UNLESS that year is also divisible by 400.

9. 1900 and 2100 are not leap years, and so are the years that are divisible by 100 but not by 400.

10. There is a leap year every year whose number is perfectly divisible by four - except for years which are both divisible by 100 and not divisible by 400.

What is true about divisible 400?

You can easily fact check it by examining the linked well-known sources.

In a year there are 365 days, unless the year it's divisible by 4, unless it's also divisible by 100, unless it's also divisible by 400. - source

A leap year does not occur every 100 years unless the year is divisible by 400 - source

Not every year divisible by 4 is a leap year. A leap year is when the year is divisible by 4 or 400 but not by 100. - source

Leap years occur every 4 years EXCEPT when the year is divisible by 100, UNLESS that year is also divisible by 400. So the years 1700, 1800, and 1900 weren't leap years, but 2000 was.

A leap year occurs every 4 years except on years divisible by 100 unless it is also divisible by 400