The word одќн 'one' sometimes corresponds to the English indefinite article 'a.' Sometimes it has the meaning 'alone' and can even be used in a plural form. It is also a numeral. Whatever its meaning, одќн is declined like a special adjective and must agree with its noun in gender, number, and case.
Онђ мнљ далђ двђдцать однџ (Acc. Sg.) копљйку (Acc. Sg.). She gave me 21 kopecks.
ТІ идќ однђ (Nom. Sg.). You go alone.
Ћн тђм познакћмился с однћй (Inst. Sg.) дљвушкой (Inst. Sg.), котћрая џчится в МГУ. He met a girl there who goes to MGU.
Дљти живџт однќ (Nom. Plur.). The children live by themselves.