The legendary BrainBashers calendar had a millennium bug. Here is a listing showing the number of days in each month:
How many days are in September?
Share link: www.brainbashers.com
Look at the first letters of the months.
The first part is the alphabetic position of the first letter of the month, S=19, the second part is the number of letters in the word itself, September=9.
Note: BrainBashers has a Dark Mode setting.