The 29th of February. It only occurs every 4 years and it is at least 12 years and can be as much as 40 years before it occurs on the same day again.
every so often but at least once a week
least three days in a week.
Thanksgiving Day falls on a Thursday in any given year.
At least once per week.
At least once a week.
At least once a week.
At least once a week.
At least once a week.
at least once a week
At least once or twice a week
In any given span of 28 years, any given day falls on any day of the week four times. In this instance, taking a span from 1985 - 2012, October 11 fell on a Friday in the following years: 1985 1991 1996 2002 For future years in which October 11 falls on a Friday, add 28 to these years.
For any given date (such as April 20), one out of every seven years it will fall on any given day of the week - at least, that's what happens in the long-term average.