Have you heard of John Conway?

John Conway was a brilliant mathematician. In addition to his vast theoretical work, he is known by many non-mathematicians for his work in recreational math, most notably for the Game of Life. There is a biography about him titled, Genius at Play, which I have not yet had a chance to read. I just found out from the Wikipedia article about him that he died last month from the corona virus.

Here is a useful scheme that Conway devised for determining the day of the week for a date in the current year. The last day of February, April 4 (4/4), 6/6, 8/8, 10/10 and 12/12. all fall on the same day of the week. This year the day is Saturday. Conway devised a scheme for odd numbered months, but it is easier to remember the phrase “working from 9 to 5 at the 7–11”. The day for May is 5/9 and the day for September is 9/5. Similarly for July and November.

The day for next year is Sunday and, in general, you add one day for non-leap years and two days for leap years.