The Golden Number can be calculated by taking the remainder of the year divided by 19 and adding 1 to it.
The Golden Number is notated using roman digits.
So, possible Golden Numbers are I, II, III, IV, ... to XIX (1 to 19).
For example: the Golden Number for the year 1999 is V [1999 mod 19 + 1 = 5].
The Golden Number is used to calculate the Epact.