φ (EN)

letter, symbol

letter “φ”

1. the 21st letter of the Greek alphabet
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   In the Greek word "φως" (light), the letter "φ" is the first character.

symbol “φ”

1. (in mathematics) the golden ratio, a special number approximately equal to 1.618 that appears in nature and art
   The ancient Greeks used φ to design buildings with pleasing proportions.
2. (in mathematics) Euler's totient function, a function that counts the numbers less than a given number that do not share any common factors with it
   To find out how many numbers less than 10 don't share factors with 10, we calculate φ(10) and find it is 4.
3. (in phonetics) a symbol used to represent a sound made by blowing air between both lips without using the vocal cords
   The sound represented by φ is found in some languages like Japanese.