by 400. Therefore, 1700 is the first century year in the Gregorian Calendar being a common year. The years 1800 and 1900 were also century common years, and so will 2100, 2200, 2300, 2500, 2600, 2700, 2900, and 3000.

The Gregorian Calendar repeats itself every 400 years, so century common years start on a Friday