A holiday puzzle is as follows. In 1995, Christmas falls
on a Monday. The puzzle is to determine how many
of the next
billion (1,000,000,000) Christmases (including 1995)
will fall on a Monday (assuming that our
current Gregorian
calendar will continue to be used). Under the Gregorian calendar
each year contains 365
days except for leap years, which contain
366. Every year divisible by 4 is a leap year except for century
years in which the year is not divisible by 400. For example,
1900 was not a leap year, but 2000 will be.
As an additional
puzzle, determine the only other day of the week to have the same
number of Christmases
as Monday during the billion years.