The reason for this problem is that Wang Xiaogang's father was born on February 29th. February is a year with 28 days in a normal year and 29 days in a leap year. There are 29 leap years in February every four years, so Wang Xiaogang's father has a birthday every four years.

Generally speaking, a leap year (from February 29th) is a leap year (for example, 2004 is a leap year), which is divisible by 4 and cannot be divisible by 100. A leap year is a century year divisible by 400 (for example, 2000 is a leap year, 1900 is not).

Reasons for leap year:

1. The earth's cycle around the sun is 365 days, 5 hours, 48 minutes and 46 seconds (365 days +09 days), that is, the year of the tropic.

2. The Gregorian calendar has an average of only 365 days a year, which is about 0.2422 days shorter than the tropic year, and the remaining time is about one day every four years. So 1 day is added at the end of February of the fourth year, making the length of that year 366 days, and this year is a leap year.

The current Gregorian calendar has 97 leap years every 400 years. According to a leap year every four years, it will count as 0.0078 days per year on average, so after 400 years, it will count as 3 days.

4. So every 400 years, three leap years will be reduced.

5. Therefore, the Gregorian calendar stipulates that when the current year is a whole hundred, it must be a multiple of 400 to be a leap year; It is not a century year with multiples of 400, and even a multiple of 4 is not a leap year.

Refer to the above? Baidu encyclopedia-leap year