## Cayley Number

There are two completely different definitions of Cayley numbers. The first type Cayley numbers is one of the eight elements in a Cayley Algebra, also known as an Octonion. A typical Cayley number is of the form

where each of the triples , , , , , , behaves like the Quaternions . Cayley numbers are not Associative. They have been used in the study of 7- and 8-D space, and a general rotation in 8-D space can be written

The second type of Cayley number is a quantity which describes a Del Pezzo Surface.

Conway, J. H. and Guy, R. K. Cayley Numbers.'' In The Book of Numbers. New York: Springer-Verlag, pp. 234-235, 1996.