the assertion about dec having something evey 800 years is wrong. the same logic for every other month with 31 days
Due to the irregularity caused by leap years, however, August does not begin on a Sunday exactly once every seven years; instead, the phenomenon follows a 6-5-6-11 pattern. That is, when August begins on Sunday, that event occurs again six years later, then five years later, then six years later, and finally eleven years later, whereupon the cycle repeats. Thus we see patterns of Sunday-beginning Augusts in clusters of years like the following:
