Numbers are quite simple in Spanish, aside from ‘uno’. While all other numbers have only one form (‘dos’, ‘tres’, ‘quince’, ‘cien’, etc.), ‘uno’ acts like an adjective and doubles as an indefinite article. That means, for example, ‘one dog’ and ‘a dog’ are translated as the same sentence in Spanish: ‘un perro’. Thus, ‘uno’ becomes ‘un’ before an masculine noun and ‘una’ before feminine one: ‘una flor’.