7, in fact, like other numbers, is regarded as a mysterious symbol by many nations and countries in the world. People in ancient Egypt, Babylon and China believed that there were seven sacred stars in the sky, namely Venus, Jupiter, Mercury, Mars, Saturn, the sun and the moon.
Because a triangle and a quadrilateral add up to seven angles, ancient Greece thought seven was a perfect number, and these two numbers were considered perfect in ancient Greece. The ancient Greeks also believed that there were four elements in nature: water, fire and earth, while human families had three elements: father, mother and son, so the world was made up of seven elements.
7 is also a number related to countless things in China traditional culture. People have seven emotions: joy, anger, worry, thinking, sadness, fear and surprise; There is the Big Dipper in the sky; Traditional festivals include the seventh day of July (Valentine's Day in China); In funeral culture, the soul of the deceased goes home in the first seven days; The other seven are the sum of yin, yang and five elements, which are related to Confucianism and Taoism.
Buddhism has seven pains in life: life, old age, illness, death, resentment, love, separation and ambition; Catholicism also has "seven deadly sins"; All this shows that 7 seems to have a very close relationship with religious culture. If we want to talk about natural phenomena, there are seven continents in the world, and the rainbow is an arched colorful spectrum.
The number 7 is also common in ancient books. Shuowen explained: "Seven, Yang is right. Inclined from a slight shadow. " Hanshu says, "Seven is the beginning of the four seasons of heaven and earth." This is to interpret 7 as a sacred number. "Yi Fu" also said, "Repeat the same thing and come back in seven days."
7 is still a unique number in the fields of science and mathematics. 1, 2, 3, 5 and 7 are all prime numbers, but the reciprocal of 1 is 1, the reciprocal of 2 is 0.5, the reciprocal of 3 is an ordinary decimal, and the reciprocal of 5 is 0.2, but the reciprocal of 7 is an infinite cycle decimal.
Whether in mathematics or culture, the number 7 seems to be full of mysterious colors and has a very close relationship with nature.