When is the next "double-13 Friday"?

[Jon Wild]

On Sat, 14 Oct 2006, Jonathan Post wrote:

>> Conjecture: The same basic repeating pattern results
>> if we seek the number of "Sunday the 22nds" or
>> "Wednesday the 8ths" or anything else similar, with
>> the only difference being that the sequence starts at
>> a different point in the repeating pattern.

I don't think your conjecture is correct, because I remember working out 
once that the 13th falls more often on a Friday than on any other day of 
the week. (This is possible because the whole 400-year cycle of the 
calendar contains a number of days that is not a multiple of 7.) So the 
number of Thursday-the-13ths, Wednesday-the-13ths, etc., per year cannot 
follow the same pattern as the number of Friday-the-13ths per year.

Jon Wild