Friendship number, that is, the mysterious number of multiples, is permeated with the special properties of some mysterious numbers in developed countries where large numbers have become common. For example, in Taoist Qigong, there are eight, sixteen, thirty-two numbers, all multiples of eight, which are rendered as sacred and unchangeable numbers. Mysterious multiples of China, such as 4, 8, 12, 24, 36, 48, 64, etc. , where 8, 24, 48, 64, 72 and 360 are all multiples of 8. Triangular number is the sum of the first n terms of a positive integer, 1, 3,6, 10,15,21,28,36,45,55,66,78, etc. For example, many logs are stacked on a construction site, and they look like triangles from the side. Pythagoras school is the art of numbers, and holds that 1 is the first principle of numbers, the mother of all things is wisdom, 2 is the principle of opposition and negation, 3 is the form and form of all things, 4 is justice, the symbol of the creator of the universe, 5 is odd and even, the combination of men and women is also marriage, 6 is the life and soul of God, 7 is opportunity and 8 is harmony.