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Later, on a calendar yet to come (we'll get to it), it was decreed that years divisible by 100 not follow the four-year leap day rule un ... 1800 and 1900, but 2000 had one. In the next 500 years ...
This eliminates 3 of the 4 end-of-century years in a 400-year period. For example, the years 1600, 2000, 2400, and 2800 are century leap years since those numbers are evenly divisible by 400, while 1700, 1800, 1900, 2100, 2200, 2300, 2500, 2600, 2700, 2900, and 3000 are common years despite being evenly divisible by 4. This scheme brings the ...
It is divisible by 4 and by 5. 480: it is divisible by 4 and by 5. 21: Subtracting twice the last digit from the rest gives a multiple of 21. (Works because (10a + b) × 2 − 21a = −a + 2b; the last number has the same remainder as 10a + b.) 168: 16 − 8 × 2 = 0. Suming 19 times the last digit to the rest gives a multiple of 21.
In the Gregorian calendar, the standard civil calendar used in most of the world, February 29 is added in each year that is an integer multiple of four, unless it is evenly divisible by 100 but not by 400. For example, 1900 was not a leap year, but 2000 was.
A year divisible by 100 is not a leap year in the Gregorian calendar unless it is also divisible by 400. For example, 1600 was a leap year, but 1700, 1800 and 1900 were not. Some programs may have relied on the oversimplified rule that "a year divisible by four is a leap year".
A century common year is a common year in the Gregorian calendar that is divisible by 100 but not by 400. Like all common years, these years do not get an extra day in February, meaning they have 365 days instead of 366. These years are the only common years that are divisible by 4.
d() is the number of positive divisors of n, including 1 and n itself; σ() is the sum of the positive divisors of n, including 1 and n itselfs() is the sum of the proper divisors of n, including 1 but not n itself; that is, s(n) = σ(n) − n
2004 – Area of the 24th crystagon [5] 2005 – A vertically symmetric number; 2006 – number of subsets of {1,2,3,4,5,6,7,8,9,10,11} with relatively prime elements [6] 2007 – 2 2007 + 2007 2 is prime [7] 2008 – number of 4 × 4 matrices with nonnegative integer entries and row and column sums equal to 3 [8] 2009 = 7 4 − 7 3 − 7 2