# Multicomplex number

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In mathematics, the multicomplex number systems $\mathbb {C} _{n}$ are defined inductively as follows: Let C0 be the real number system. For every n > 0 let in be a square root of −1, that is, an imaginary unit. Then $\mathbb {C} _{n+1}=\lbrace z=x+yi_{n+1}:x,y\in \mathbb {C} _{n}\rbrace$ . In the multicomplex number systems one also requires that $i_{n}i_{m}=i_{m}i_{n}$ (commutativity). Then $\mathbb {C} _{1}$ is the complex number system, $\mathbb {C} _{2}$ is the bicomplex number system, $\mathbb {C} _{3}$ is the tricomplex number system of Corrado Segre, and $\mathbb {C} _{n}$ is the multicomplex number system of order n.
Each $\mathbb {C} _{n}$ forms a Banach algebra. G. Bayley Price has written about the function theory of multicomplex systems, providing details for the bicomplex system $\mathbb {C} _{n}.$ The multicomplex number systems are not to be confused with Clifford numbers (elements of a Clifford algebra), since Clifford's square roots of −1 anti-commute ($i_{n}i_{m}+i_{m}i_{n}=0$ when mn for Clifford).
Because the multicomplex numbers have several square roots of –1 that commute, they also have zero divisors: $(i_{n}-i_{m})(i_{n}+i_{m})=i_{n}^{2}-i_{m}^{2}=0$ despite $i_{n}-i_{m}\neq 0$ and $i_{n}+i_{m}\neq 0$ , and $(i_{n}i_{m}-1)(i_{n}i_{m}+1)=i_{n}^{2}i_{m}^{2}-1=0$ despite $i_{n}i_{m}\neq 1$ and $i_{n}i_{m}\neq -1$ . Any product $i_{n}i_{m}$ of two distinct multicomplex units behaves as the $j$ of the split-complex numbers, and therefore the multicomplex numbers contain a number of copies of the split-complex number plane.
With respect to subalgebra $\mathbb {C} _{k}$ , k = 0, 1, ..., n − 1, the multicomplex system $\mathbb {C} _{n}$ is of dimension 2nk over $\mathbb {C} _{k}.$ 