Merriam-Webster's Advanced Learner's Dictionary:
thirteen
thir·teen /ˌɵɚˈtiːn/ noun, pl -teens [count] : the number 13
- thirteen adj
• thirteen students
- thirteen pronoun
• All thirteen (of them) passed the exam.
- thir·teenth /ˌɵɚˈtiːnɵ/ noun, pl -teenths [count]
• the thirteenth of October
• one thirteenth of the budget
- thirteenth adj
• the thirteenth caller
- thirteenth adv
• She finished thirteenth.
• the nation's thirteenth largest city
