Wikipedia:Reference desk/Archives/Mathematics/2019 November 11

= November 11 =

Four consecutive years with two Friday the 13ths each
The years 2017, 2018, 2019, and 2020 are four consecutive years with two Friday the 13ths each (Jan 13 and Oct 13, Apr 13 and Jul 13, Sep 13 and Dec 13, and Mar 13 and Nov 13 respectively). Is it true that any four consecutive years with two Friday the 13ths each in either the Julian calendar or the Gregorian calendar must end with a leap year starting on Wednesday (or equivalently, with one exception in each 400-year period, consist of the next four consecutive years following a leap year starting on Friday)? If so, then it follows that the table below is complete.

The exception is the year 2196. Adding 4 years to 2196 gives the non-leap century 2200, which has a Friday the 13th in June. Hence, the years 2197, 2198, 2199, and 2200 are not included in the above table. GeoffreyT2000 (talk) 06:39, 11 November 2019 (UTC)


 * I think that you are probably right. Bubba73 You talkin' to me? 16:03, 11 November 2019 (UTC)