Uno, masculine Una, feminine
No, you don't need to say, except you want to say "I won, Uno :P" or else. Uno (Spanish, Italian) is One. So, you must to say it when only one card left in your hand. :)
Mil setecientos ochenta y uno
Treinta y uno
We don't usually say "nueve uno uno" or "nueve once." We native speakers say "novescientos once."
You can say "sólo uno".
1821 = mil ocho-cientos veinte-uno
Uno
¿Quieres uno? - informal ¿Usted quiere uno? - formal
To say UNO!!After all your cards are gone and before the next player plays.
Le UNO
UNo Sinco