At market close:
a will be the integer part of the percentage of this market as is displayed on the site. (57.9% internally is shown as 58 so 58 would be used. For 99.5%, I would use 99 and 0.5% would be 0)
n will be the number of shareholders if it is odd, or 1 more than that if it is even.

The market resolves according to the value Jacobi(x,p):

1: resolves YES,

-1: resolves NO,

0: resolves N/A

For the definition, you can check https://en.wikipedia.org/wiki/Jacobi_symbol

Based of the same market for the Legendre Symbol: