Article: Nouns are also inflected for number, distinguishing between singular and plural. Typical of a Slavic language, Czech cardinal numbers one through four allow the nouns and adjectives they modify to take any case, but numbers over five place these nouns and adjectives in the genitive case when the entire expression is in nominative or accusative case. The Czech koruna is an example of this feature; it is shown here as the subject of a hypothetical sentence, and declined as genitive for numbers five and up.

Now answer this question: What are inflected for number in Czech?
Nouns