The number π (spelled out as pi) is a mathematical constant, approximately equal to 3.14159, that is the ratio of a circle's circumference to its diameter. The number π is an irrational number, meaning that it cannot be expressed exactly as a ratio of two integers, although fractions such as 22/7. are commonly used to approximate it. Consequently, its decimal representation never ends, nor does it enter a permanently repeating pattern. (Wikipedia) Also apparently it's the 16th letter of the Greek alphabet. The more you know.
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