00, 28, 56, 84 etc.
The significance of 28 to this technique is that the calendar within a century repeats itself every 28 years. (7 days in a week, 4 weeks in a leap-year cycle, 7 x 4 = 28.) So the calendar for 1901 is the same as for 1929, 1957 and 1985. The only exception to this is Jan/Feb in turn-of-the-century years ('00) that are not divisible by 400 (e.g., 1700, 1800, 1900, 2100).
