I watched a documentary and in that production reference was made to the golden number.  I still don’t understand. 

golden number (sometimes capitalized) is a number assigned to each year in sequence to indicate the year’s position in a 19-year Metonic cycle. They are used in the computus (the calculation of the date of Easter) and also in the Runic calendar. The golden number of any Julian or Gregorian calendar year can be calculated by dividing the year by 19, taking the remainder, and adding 1. (In mathematics this can be expressed as (year number modulo 19) +1.)

For example, 2016 divided by 19 gives 106, remainder 2. Adding 1 to the remainder gives a golden number of 3.

The term golden number is first documented in the computistic poem Massa Compoti by Alexander de Villa Dei in 1200.[1]Later, a scribe added it to tables originally composed by Abbo of Fleury in 988.