By analogy, you will find that the last number is equal to the sum of the first two numbers. The numbers in this series are called Fibonacci numbers. 2 is the third Fibonacci number. Phenomenon: This series is closely related to natural plants. The number of petals of almost all flowers comes from one number in this series: the square scales and bracts of pineapple skin form two groups of spirals with opposite directions, and their numbers must be the next two numbers in this series (such as left-handed 8 lines and right-handed 13 lines); There is also a sunflower disk ... if the two sets of spirals are exactly the same, wouldn't it be more strictly symmetrical? But nature is partial! It was not until recently 1993 that people gave this ancient and important series a truly satisfactory explanation: the ratio of any two adjacent numbers in this series, divided by the second order, is the closest to the value of 0.6 18034 ... and its limit is the so-called "golden section number".