Pi necklace. Greece letter jewelry. The mathematical constant Pi is a real number and can be defined as the ratio length of the circumference of a circle to its diameter in Euclidean geometry, and is used very often in mathematics, physics and engineering. The symbolism comes from the first letter of the word region ( Περιφέρεια - Periferia in Greek, Π - Pi) and has established itself internationally. In the Latin alphabet is represented as Pi when Greek characters are not available. Pi is also known as Archimedes constant. *NOTICE* Titanium is an hypoallergenic material and its the same that used in surgery. It is absolutely safe and causes no any allergies at all. The chain is made of sterling silver so unless you have a sterling silver allergy you can fully enjoy wearing this!!! I try to ensure that my photos are accurate, but please remember various monitors will display colors slightly differently, so the color may not match exactly what you see on the screen. Thanks for looking! Teacher gift ideas