CARDINAL NUMERALS (from 0 to 20)
CARDINAL NUMERALS (from 21 to 100)
*Note that your set of ten (venti, trenta, quaranta, ecc.) will drop its final vowel if it is combined with uno or otto: ventuno, quarantotto, cinquantuno.
**Note that numbers ending in –tré (except for tre itself) have an accent: ventitré, settantatré, duecentotré.
CARDINAL NUMERALS (from 101 to 1,000,000,000)
Notes on cardinal numbers:
Cardinal numbers are invariable. E.g., “Ha passato trenta giorni in vacanza,” “Ho quattro libri.”
Mille is ‘one thousand’ while “-mila” is the invariable form for all multiples of ‘thousand,’ like duemila, tremila, quindicimila, etc…
Numbers are written together until 999,999. Eg.: novecentonovantanovemilanovecentonovantanove From 1,000,000 on, they are separated at the millions, billions, trillions . Eg: due milioni e trecentoquattromila.
for million(s), milione, and billion(s), miliardo, you add di before the noun only if the number is a ‘direct/whole’ number like “one million soldiers,” (without modifications like “one million three hundred thousand soldiers”), e.g., un milione di soldati, tre miliardi di euro.
If there are modifications (like two billion seven hundred million euros) then you do not add di before the noun, e.g., a) un milione trecento mila soldati; b) due miliardi settecento milioni e ventiduemila persone.