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Challenge Response 176


Is there Friday 13 every year?

There are 14 different calendars. There are seven possible calendars for non-leap years (one with January 1 for each day of the week).

The leap years have seven more calendars, resulting in a total of 14. For example, if January 1 is a Wednesday, we have:

January 1st - Wednesday
January 13th - Monday
February 1st - Saturday
February 13th - Thursday
March 1st - Saturday
March 13 - Thursday
April 1st - Tuesday
April 13 - Sunday
May 1st - Thursday
May 13th - Tuesday
June 1st - Sunday
June 13th - Friday
Since June 13 is a Friday, you can stop. The following table shows the total number of Fridays 13 for all calendars.

When January 1st falls in Months of leap years with a friday 13 Months leap years with a friday 13
MondayApril, JulySeptember December
TuesdaySeptember DecemberJune
WednesdayJuneMarch, November
ThursdayFebruary, March, NovemberFebruary, August
FridayAugustMay
SaturdayMayOctober
SundayJanuary, OctoberJanuary, April, July

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