Numbers have two forms

• cardinal, which indicate the quantity of something
  • sixty-seven dollars
• ordinal, which indicate the order of things
  • the sixty-seventh dollar

Numbers are mostly adjectives. Sometimes they are used as nouns (most often mille and primus).

No source has said this, but I'm assuming that for compounds, each part does its own thing in declination (like the quid and dam in quidam).

Cardinal

Most cardinals are undeclined.

unus

unus is declined like a 1/2dec -ius adjective.

	M	F	N	M PL	F PL	N PL
nom	unus	una	unum	uni	unae	una
acc	unum	unam	unum	unos	unas	una
gen	unius	unius	unius	uni	unae	uni
dat	uni	uni	uni	unis	unis	unis
abl	uno	una	uno	unis	unis	unis

The plural is necessary because:

• unus also means same or only
• to agree with plural only nouns of a singular meaning
  • una balena? one bathhouse?

duo

duo is PL only and irregular.

	M PL	F PL	N PL
nom	duo	duae	duo
acc	duos | duo	duas	duo
gen	duorum	duarum	duorum
dat	duobus	duabus	duobus
abl	duobus	duabus	duobus

tres

tres is PL only and declined like a 3rd declension i-stem adjective. it's two-termination.

	M/F PL	N PL
nom	tres	tria
acc	tres | tris	tria
gen	trium	trium
dat	tribus	tribus
abl	tribus	tribus

hundreds

200, 300, 400, 500, 600, 700, 800, 900, are declined like first declension plural only adjectives.

mille

mille is singular only. The plural meaning is supplied by the NT PL noun mīlia, mīlium, plus the genitive of whatever thing you're describing.

• mille homines
• mille hominum (with mille as a noun)
• duo milia hominum
• cum duobus milibus hominum (note how octo is a numerical adjective that describes milibus - we have come full circle)

milia, milium is also found with a double L (millia, millium)

(n mod 10) = (8 or 9)

?? (I copy and pasted this)

The forms octōdecim, novendecim are rare, duodēvīgintī (two from twenty), ūndēvīgintī (one from twenty), being used instead. So 28, 29; 38, 39; etc. may be expressed either by the subtraction of two and one or by the addition of eight and nine respectively.

• how would you express subtraction????
• et is addition

Ordinal

Everything is declined like first declension adjectives. Example:

• secundus, secunda, secundum
• alter, altera, alterum

Ordinals ending in -ēnsimus are often written without n

• vīcēnsimus → vīcēsimus

Reference Sheet

decimal	hex	binary	CARDINAL	ORDINAL	ROMAN NUMERALS
1	1	1	ūnus	prīmus	I
2	2	10	duo	secundus | alter	II
3	3	11	trēs	tertius	III
4	4	100	quattuor	quārtus	IIII or IV
5	5	101	quīnque	quīntus	V
6	6	110	sex	sextus	VI
7	7	111	septem	septimus	VII
8	8	1000	octō	octāvus	VIII
9	9	1001	novem	nōnus	VIIII or IX
10	A	1010	decem	decimus	X
11	B	1011	ūndecim	ūndecimus	XI
12	C	1100	duodecim	duodecimus	XII
13	D	1101	tredecim; decem (et) trēs	tertius decimus; decimus (et) tertius	XIII
14	E	1110	quattuordecim	quārtus decimus	XIIII or XIV
15	F	1111	quīndecim	quīntus decimus	XV
16	10	1,0000	sēdecim	sextus decimus	XVI
17	11	1,0001	septendecim	septimus decimus	XVII
18	12	1,0010	duodēvīgintī; octōdecim	duodēvīcēnsimus; octāvus decimus	XVIII
19	13	1,0011	ūndēvīgintī; novendecim	ūndēvīcēnsimus; nōnus decimus	XVIIII or XIX
20	14	1,0100	vīgintī	vīcēnsimus; vīgēnsimus	XX
21	15	1,0101	vīgintī ūnus; ūnus (et) vīgintī	vīcēnsimus prīmus; ūnus (et) vīcēnsimus	XXI
30	1E	1,1110	trīgintā	trīcēnsimus	XXX
40	28	10,1000	quadrāgintā	quadrāgēnsimus	XXXX or XL
50	32	11,0010	quīnquāgintā	quīnquāgēnsimus	↓ or L
60	3C	11,1100	sexāgintā	sexāgēnsimus	LX
70	46	100,0110	septuāgintā	septuāgēnsimus	LXX
80	50	101,0000	octōgintā	octōgēnsimus	LXXX
90	5A	101,1010	nōnāgintā	nōnāgēnsimus	LXXXX or XC
100	64	110,0100	centum	centēnsimus	C
101	65	110,0101	centum (et) ūnus	centēnsimus prīmus	CI
200	C8	1000,1000	ducentī	ducentēnsimus	CC
300	12C	1,0010,1100	trecentī	trecentēnsimus	CCC
400	190	1,1001,0000	quadringentī	quadringentēnsimus	CCCC
500	1F4	1,1111,0100	quīngentī	quīngentēnsimus	D
600	258	10,0101,1000	sescentī	sescentēnsimus	DC
700	2BC		septingentī	septingentēnsimus	DCC
800			octingentī	octingentēnsimus	DCCC
900			nōngentī	nōngentēnsimus	DCCCC
1000			mīlle	mīllēnsimus	∞ (CIϽ) or M
5000			quīnque mīlia	quīnquiēns mīllēnsimus	IϽϽ
10,000	3E8		decem mīlia	deciēns mīllēnsimus	CCIϽϽ
100,000			centum mīlia	centiēns mīllēnsimus	CCCIϽϽϽ

references

https://dcc.dickinson.edu/grammar/latin/declension-cardinals-and-ordinals