Răspuns :

[tex]\it D_{20}=\{1,\ 2,\ 4,\ 5,\ 10,\ 20\},\ \ card(D_{20})=6\\ \\ \\ \overline{23x}\ \vdots\ 2 \Rightarrow\ x=\ cifr\breve a\ par\breve a \Rightarrow numerele\ cerute\ sunt: 230,\ 232,\ 234,\ 236,\ 238\\ \\ \\ 729\ \vdots\ 3[/tex]