Remember that while there are 14 patterns of years, leap years don't
impact Friday the 13th for January/February..
This isn't an exhaustive analysis, but a quick check for 300 years
didn't show any years without a Friday 13th..
;-)
$ for y in {1900..2199} ; do for m in {1..12};do cal $m $y|awk 'FNR==1{m=$0}/^
1/{print m}';done;done | awk '{y[$2]++} END {for (i=1900;i<2200;i++) if (!(i in
y)) print i}'
$
Happy New Year!
On Mon, Dec 21, 2015 at 10:13:38AM -0500, Greg Wooledge wrote:
> 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.
>
--
Bill Duncan,
bdun...@beachnet.org
+1 416 697-9315
