calendar calculation
the rare ability to identify the day of the week for any given date, such as February 19, 1878, in a matter of seconds. Calendar calculators are frequently savants who usually have no evident mathematical ability but may be able to perform other feats with the calendar, such as correctly answering the question, “In what years did April 16 fall on a Sunday?” No satisfactory explanation has been found for this skill. See also idiot savant.