Golden number

(chronology) A number showing the year of the lunar or Metonic cycle. It is reckoned from 1 to 19, and is so called from having formerly been written in the calendar in gold.

The irrational number (approximately 1.618), usually denoted by the Greek letter φ (phi), which is equal to the sum of its own reciprocal and 1, or, equivalently, is the square root of the sum of itself and 1.