According to the Julian calendar, the year in which there is February 29, and the number of days is 366, is called a leap year. Every fourth year, one more day is added to the usual 28 days of February. However, this algorithm for calculating the leap year after the adoption of the Gregorian calendar in 1582 should be changed.
Divide the numerical value of the year by 4. Years that are not divisible by 4 are not leap years.
2008/4 = 502
2011/4 = 502, 75
2008 is a leap year (divisible with no remainder), according to the rule of step 1, 2011 is not a leap year (divisible with a remainder).
After successfully completing step 1, you must divide the numerical value of the year by 100.
If a year is divisible by 100 without a remainder, that year will not be a leap year, even if it was successfully divided by 4.
2104/4 = 526
2104 / 100 = 21, 04
The year 2104 is a multiple of 4, but not a multiple of 100 (when dividing, the remainder is obtained).
According to the rule of step 2, it is a leap year. 2100/4 = 525
2100 / 100 = 21
The year 2100 is a multiple of 4, but a multiple of 100. According to the rule of step 2, it is not a leap year.
But there may be exceptions here too. For an accurate calculation, follow step 3.
It is necessary to divide the year, the numerical value of which turned out to be a multiple of 4 and 100, by 400. If it is divided without a remainder, then the year is, after all, a leap year!
2100/4 = 525
2100 / 100 = 21
2100 / 400 = 5, 25
2100 is not a multiple of 400, which means, according to all the rules, it is not a leap year 2000/4 = 500
2000 / 100 = 20
2000 / 400 = 5
Year 2000 is divisible by 4, by 100, but also by 400. Therefore, according to the rule of step 3, it is a leap year.