Supernatural number

In mathematics, the supernatural numbers, sometimes called generalized natural numbers or Steinitz numbers, are a generalization of the natural numbers.

They were used by Ernst Steinitz[1]: 249–251  in 1910 as a part of his work on field theory.

A supernatural number

ω

is a formal product: where

runs over all prime numbers, and each

is zero, a natural number or infinity.

( ω )

and there are only a finite number of non-zero

then we recover the positive integers.

Slightly less intuitively, if all

[citation needed] Supernatural numbers extend beyond natural numbers by allowing the possibility of infinitely many prime factors, and by allowing any given prime to divide

ω

"infinitely often," by taking that prime's corresponding exponent to be the symbol

There is no natural way to add supernatural numbers, but they can be multiplied, with

Similarly, the notion of divisibility extends to the supernaturals with

The notion of the least common multiple and greatest common divisor can also be generalized for supernatural numbers, by defining and With these definitions, the gcd or lcm of infinitely many natural numbers (or supernatural numbers) is a supernatural number.

We can also extend the usual

-adic order functions to supernatural numbers by defining

Supernatural numbers are used to define orders and indices of profinite groups and subgroups, in which case many of the theorems from finite group theory carry over exactly.

They are used to encode the algebraic extensions of a finite field.

[2] Supernatural numbers also arise in the classification of uniformly hyperfinite algebras.