Generally, a noun phrase with a number but without 这 or 那 is considered indefinite. However, note that such a noun phrase, when in context, can actually be definite.
zhuō shàng yǒu liǎng běn shū ；yī běn shì wǒ de ，yī běn shì tā de 。
There are two books on the table; one (of them) is mine; one (of them) is his.
(两本书 is indefinite. In this context, 一本 is definite and, therefore, can serve as the subject of the sentence 一本是我的.)
 Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.