On Mon, Dec 21, 2015 at 02:59:20PM +0000, Allodoxaphobia wrote: > Is the logic exhaustive ? -- in that it shows there > are no years with *no* Friday The 13Th's?
The Gregorian calendar has 14 different year layouts: 7 non-leap-years beginning with Sunday through Saturday, and 7 leap-years beginning with Sunday through Saturday. To prove your assertion, it is sufficient to count the number of Friday the 13ths in each of those 14 layouts.
