# Pi Day Countdown #13 – Pi and the Periphery

$\pi$ is among the oldest and most famous constant of mathematics, however as a number it wasn’t called $\pi$ until the early 18th century.

Before $\pi$ was known as the number defined as the circumference of a circle divided by its diameter. However, in 1706 self taught mathematics teach William Jones labeled the constant $\pi$ in his book “Synopsis Palmariorum Matheseos” (a new introduction to mathematics). Perhaps he named it this because $\pi$ was Greek for p which would be first letter of the word periphery.

This notation was then popularized by the famous Swiss mathematician, Leonhard Euler in 1738, two decades after $\pi$‘s official naming.

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