Tuple

Tuple length, ${\displaystyle n}$	Name	Alternative names
0	empty tuple	null tuple / empty sequence / unit / none left
1	monuple	single / singleton / monad
2	couple	double / ordered pair / two-ple / twin / dual / duad / dyad / twosome
3	triple	treble / triplet / triad / ordered triple / threesome
4	quadruple	quad / tetrad / quartet / quadruplet
5	quintuple	pentuple / quint / pentad
6	sextuple	hextuple / hexad
7	septuple	heptuple / heptad
8	octuple	octa / octet / octad / octuplet
9	nonuple	nonad / ennead
10	decuple	decad / decade (antiquated)
11	undecuple	hendecuple / hendecad
12	duodecuple	dozen / duodecad
13	tredecuple	baker's dozen
14	quattuordecuple	double septuple
15	quindecuple	triple quintuple
16	sexdecuple	quadruple quadruple
17	septendecuple	N/A
18	octodecuple	Double Nonuple
19	novemdecuple	N/A
20	vigintuple	Quadruple Quintuple
21	unvigintuple	Triple Septuple
22	duovigintuple	Double Undecuple
23	trevigintuple	N/A
24	quattuorvigintuple
25	quinvigintuple
26	sexvigintuple
27	septenvigintuple
28	octovigintuple
29	novemvigintuple	N/A
30	trigintuple
31	untrigintuple	N/A
32	duotrigintuple	Double Sexdecuple
40	quadragintuple
50	quinquagintuple
60	sexagintuple
70	septuagintuple
80	octogintuple
90	nongentuple
100	centuple
1,000	milluple	chiliad

Note that for ${\displaystyle n\geq 3}$, the tuple name in the table above can also function as a verb meaning "to multiply [the direct object] by ${\displaystyle n}$"; for example, "to quintuple" means "to multiply by 5". If ${\displaystyle n=2}$, then the associated verb is "to double". There is also a verb "sesquiple", meaning "to multiply by 3/2". Theoretically, "monuple" could be used in this way too.

The ${\displaystyle 0}$-tuple may be identified as the empty function. For ${\displaystyle n\geq 1,}$ the ${\displaystyle n}$-tuple ${\displaystyle \left(a_{1},\ldots ,a_{n}\right)}$ may be identified with the (surjective) function

${\displaystyle F~:~\left\{1,\ldots ,n\right\}~\to ~\left\{a_{1},\ldots ,a_{n}\right\}}$

with domain

${\displaystyle \operatorname {domain} F=\left\{1,\ldots ,n\right\}=\left\{i\in \mathbb {N} :1\leq i\leq n\right\}}$

and with codomain

${\displaystyle \operatorname {codomain} F=\left\{a_{1},\ldots ,a_{n}\right\},}$

that is defined at ${\displaystyle i\in \operatorname {domain} F=\left\{1,\ldots ,n\right\}}$ by

${\displaystyle F(i):=a_{i}.}$

That is, ${\displaystyle F}$ is the function defined by

${\displaystyle {\begin{alignedat}{3}1\;&\mapsto &&\;a_{1}\\\;&\;\;\vdots &&\;\\n\;&\mapsto &&\;a_{n}\\\end{alignedat}}}$

in which case the equality

${\displaystyle \left(a_{1},a_{2},\dots ,a_{n}\right)=\left(F(1),F(2),\dots ,F(n)\right)}$

necessarily holds.

Tuples as sets of ordered pairs

Functions are commonly identified with their graphs, which is a certain set of ordered pairs. Indeed, many authors use graphs as the definition of a function. Using this definition of "function", the above function ${\displaystyle F}$ can be defined as:

${\displaystyle F~:=~\left\{\left(1,a_{1}\right),\ldots ,\left(n,a_{n}\right)\right\}.}$

Another way of modeling tuples in Set Theory is as nested ordered pairs. This approach assumes that the notion of ordered pair has already been defined.

1. The 0-tuple (i.e. the empty tuple) is represented by the empty set ${\displaystyle \emptyset }$.
2. An n-tuple, with n > 0, can be defined as an ordered pair of its first entry and an (n − 1)-tuple (which contains the remaining entries when n > 1):

   ${\displaystyle (a_{1},a_{2},a_{3},\ldots ,a_{n})=(a_{1},(a_{2},a_{3},\ldots ,a_{n}))}$

This definition can be applied recursively to the (n − 1)-tuple:

${\displaystyle (a_{1},a_{2},a_{3},\ldots ,a_{n})=(a_{1},(a_{2},(a_{3},(\ldots ,(a_{n},\emptyset )\ldots ))))}$

Thus, for example:

${\displaystyle {\begin{aligned}(1,2,3)&=(1,(2,(3,\emptyset )))\\(1,2,3,4)&=(1,(2,(3,(4,\emptyset ))))\\\end{aligned}}}$

A variant of this definition starts "peeling off" elements from the other end:

1. The 0-tuple is the empty set ${\displaystyle \emptyset }$.
2. For n > 0:

   ${\displaystyle (a_{1},a_{2},a_{3},\ldots ,a_{n})=((a_{1},a_{2},a_{3},\ldots ,a_{n-1}),a_{n})}$

This definition can be applied recursively:

${\displaystyle (a_{1},a_{2},a_{3},\ldots ,a_{n})=((\ldots (((\emptyset ,a_{1}),a_{2}),a_{3}),\ldots ),a_{n})}$

Thus, for example:

${\displaystyle {\begin{aligned}(1,2,3)&=(((\emptyset ,1),2),3)\\(1,2,3,4)&=((((\emptyset ,1),2),3),4)\\\end{aligned}}}$

Using Kuratowski's representation for an ordered pair, the second definition above can be reformulated in terms of pure set theory:

1. The 0-tuple (i.e. the empty tuple) is represented by the empty set ${\displaystyle \emptyset }$;
2. Let ${\displaystyle x}$ be an n-tuple ${\displaystyle (a_{1},a_{2},\ldots ,a_{n})}$, and let ${\displaystyle x\rightarrow b\equiv (a_{1},a_{2},\ldots ,a_{n},b)}$. Then, ${\displaystyle x\rightarrow b\equiv \{\{x\},\{x,b\}\}}$. (The right arrow, ${\displaystyle \rightarrow }$, could be read as "adjoined with".)

In this formulation:

${\displaystyle {\begin{array}{lclcl}()&&&=&\emptyset \\&&&&\\(1)&=&()\rightarrow 1&=&\{\{()\},\{(),1\}\}\\&&&=&\{\{\emptyset \},\{\emptyset ,1\}\}\\&&&&\\(1,2)&=&(1)\rightarrow 2&=&\{\{(1)\},\{(1),2\}\}\\&&&=&\{\{\{\{\emptyset \},\{\emptyset ,1\}\}\},\\&&&&\{\{\{\emptyset \},\{\emptyset ,1\}\},2\}\}\\&&&&\\(1,2,3)&=&(1,2)\rightarrow 3&=&\{\{(1,2)\},\{(1,2),3\}\}\\&&&=&\{\{\{\{\{\{\emptyset \},\{\emptyset ,1\}\}\},\\&&&&\{\{\{\emptyset \},\{\emptyset ,1\}\},2\}\}\},\\&&&&\{\{\{\{\{\emptyset \},\{\emptyset ,1\}\}\},\\&&&&\{\{\{\emptyset \},\{\emptyset ,1\}\},2\}\},3\}\}\\\end{array}}}$