There are many claims for the first use of the symbol for pi (π). English mathematician William Oughtred (1575–1660) in 1647, wrote it “p.d.” But the symbol also meant a number of other things in other texts, including a point, a positive number, and sundry other representations. The modern use of π didn’t occur until 1706, when Welsh mathematician William Jones (1675–1749) described it as, “3.12159 and c. = π” [sic]. Even then, not everyone used it as a standard symbol for pi. By 1737, Swiss mathematician Leonhard Euler (1707–1783), one of the most prolific mathematicians who ever lived, adopted the symbol in his work, making π a standard notation since that time.