Most devices use three line segments, but devices made by some Japanese companies such as Sharp and Casio, as well as in the Koreas and Taiwan, 7 is written with four line segments because in those countries, 7 is written with a "hook" on the left, as ① in the following illustration.
The number 7 is often considered lucky, and it has a definite mystique, perhaps because it is a prime number—that is, it cannot be obtained by multiplying two smaller numbers together.
Road sign in British Columbia showing the use of 7 to represent ʔ. The forty-first letter of the Squamish alphabet, written in the Latin script.
Your guide to the number 7, an odd number which is prime. Mathematical info, prime factorization, fun facts and numerical data for STEM, education and fun.
Number 7 is the number of perfection, security, safety and rest. Seven contains the number three of the heavens and soul with the number four of the earth and body. The Pythagoreans called the number 7 “the Septad”. The seven colors of the rainbow.