第十三 is the ordinal number 'thirteenth', formed by prefixing 第 (dì, marker of order) to 十三 (thirteen). In standard Chinese, ordinals are not measure words, but the source data lists the POS as 'm' (classifier/measure word), which is likely a labeling error. You can use 第十三 directly as a modifier or standalone ordinal: 他是第十三 ('He is the 13th').