Question

Why some millenial years are not leap year?

Answer 1

In the Gregorian calendar every year that is divisible by 400 is due to be an end-of-century leap year (often called a century leap year), with the intercalation of February 29 yielding 366 days instead of 365. End-of-century years that are notdivisible by 400 are common years (with 365 days) and not leap years.