The **inphixillion** is a number introduced as **tier googolillion** illion^{[1]}. The term was coined by Trakaplex. Just like *schmittyillion*, it was first clarified on Googology Testing Wiki^{[2]} without a precise definition, and was later described on an answers.com post as "in tier googolillion (10^(3*googol+3))".^{[1]} There has been rumors that the creator has been working on an illion disastrously larger, but no word has slipped yet.

## Issue

The number was introduced as 10^{(3*10↑↑103*10100+3)110,101,011(↓↓103*10100+3-1)+3}, but the unary operation ↓↓ is undefined.^{[3]} Since ↓↓ itself is not defined on numbers, one needs to precisely formalise a notation including ↑↑ and ↓↓. Moreover, the creator tends to write (3*10↑↑b)^{c} even if it is not intended to be the c-th power of 3×(10↑↑b) or 3 times the c-th power of 10↑↑b. It perhaps means a value of the sequence \(a_n\) introduced in "Alternative definition" section.

According to the creator, the definition means "a googolillion 3*10 base exponents raised to the 110101011 back down a googolillion bases plus three", which is still ambiguous. Perhaps it can be described in a way similar to schmittyillion#Alternative definition, as we will explain in "Alternative definition" section.

## Alternative definition

Considering the creator's explanations, the intended value of the number is perhaps given as \(10^{a_{\textrm{googolillion}}+3}\) using the sequence \((a_n)_{n=1}^{\infty}\) defined in the following recursive way:

- If \(n = 1\), then \(a_n := 3 \times 10^{110101011}\)
- If \(n > 1\), then \(a_n := 3 \times 10^{a_{n-1}}\)

Readers should be careful that \(a_n\) is not something like \(3 \times (10 \uparrow \uparrow n)^{110101011}\) or \(((3 \times 10) \uparrow \uparrow n)^{110101011}\), although the creator used the expression (3*10↑↑10^{3*10100+3})^{110,101,011}. According to the creator, this alterntive definition is compatible with the creator's intention.^{[4]}

More generally, define a map \begin{eqnarray*} f \colon \mathbb{N}^2 & \to & \mathbb{N} \\ (x,y) & \mapsto & f(x,y) \end{eqnarray*} in the following recursive way:

- If \(y = 0\), then \(f(x,y) := x\)
- If \(y > 0\), then \(f(x,y) := 3 \times 10^{f(x,y-1)}\).

Then the alternative definition of schmittyillion is equivalent to \(10^{f(4182001,\textrm{googol})+3}\), and the alternative definition of inphixillion is equivalent to \(10^{f(110101011,\textrm{googolillion})+3}\).

## Etymology

It is based off 'inphixinity' and the word 'illion'.

## Sources (in progress)

- ↑
^{1.0}^{1.1}what is the biggest known number Answers.com. 1/18/2021. - ↑ Inphixillion. Googology Testing Wiki. 1/18/2021.
- ↑ Trakaplex, A comment explaining ↓↓ but clarifying the lack of the definition, Googology Wiki user blog.
- ↑ A difference page of the talk page of this article.