For the perfect party, invite a mathematician. A mathematical theory predicts how large a gathering of people must become before it inevitably breaks down into cliques of mutual interest and mutual dislike.

The same mathematical column has the following tidbit which I find fascianting (and am clipping and saving) but is guaranteed to have only limited appeal, I fear:

Is there
a formula for working out the day of the week
corresponding to a date of birth?

Indeed there is. Suppose the date is September 23,
1959. First, take the final two digits of the year (in
this case, 59), divide them by four, ignoring any
remainder (14), and add the result to the original
two digits (giving 73). Now add to this the day of
the month (23) and divide the result by seven, this
time keeping only the remainder (five).

Next, add the “month number”: six for January (five
in leap years), two for February (one in leap years);
two for March; five for April; zero for May; three for
June; five for July; one for August; four for
September; six for October; two for November; four
for December. Finally, add two and divide the result
by seven, again keeping only the remainder. The
result is the day of the week on which you were
born, starting from one for Sunday. So September
23, 1959, was a Wednesday. The Telegraph

[If you try this for dates >12/31/99, instead of using just the last two digits of the year, you have to use the number of years since 1900, i.e. ‘100’ for the year 2000 etc.]