Under the Gregorian reform, which century years still count as leap years?

1. The Julian rule gave every fourth year an extra day, which was slightly too generous. 2. Gregory dropped the extra day from three out of every four century years. 3. Only century years divisible by 400 kept it, so 1600 and 2000 were leap years. 4. The years 1700, 1800 and 1900 divide by 4 but not by 400, so they were common years. _Source: OpenStax Astronomy (CC BY 4.0), Ch 4 "Earth, Moon, and Sky" and Ch 5 "Radiation and Spectra", section 4.4 The Calendar_