Leonhard Euler (pronounced Oiler as ccunning points out) was born in 1707 at

Basle,

Switzerland. At the age of 20 having already graduated from Basle University, he moved to

St. Petersburg where within ten years he became professor of

physics and

mathematics. For a while he taught in

Berlin but towards the end of his life, beset by total

blindness yet still able to perform astounding mathematical feats in his head, he returned to Russia where he taught until his death at the age of 76.

One of the greatest mathematicians to have ever lived, his many published works dealt with the diverse subjects of number theory, geometry, calculus (still a new and unproven concept then), astronomy and physics. His name lives on through a number of important mathematical concepts:

**Euler's Constant** (usually denoted by the Greek letter gamma γ) is the limit, as *n*->*s*, of 1 + ^{1}/_{2} + ^{1}/_{3} + ^{1}/_{4} *n* -> infinity ... ^{1}/_{n} - log_{e}*n*, approximately 0.577.

**Euler's Function** (denoted by φ(*n*)) refers in the number of integers in the set 1,2,3,...,*n*-1 which are prime to *n*; thus φ(9) = 6, since 6 of the integers 1,2,3,...8 are prime to 9.

**Euler's Formula for Polyhedra** states that if a polyhedron has *v* vertices, *f* faces and *e* edges, *v* + *f* - *e* = 2 for all polyhedra; thus a cube has 8 vertices, 12 edges and 6 faces, and 8 + 6 - 12 = 2.