Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
trĕdĕcim (tresd-, Front. Aquaed. 33), num. adj. [tres-decem], thirteen: tredecim captis navibus, Liv. 36, 45, 3: centum tredecim senatores, Tac. H. 5, 19 fin.: equus emptus talentis tredecim, Gell. 5, 2, 2 (for which we have decem et tres, Cic. Rosc. Am. 7, 20: decem tres, Liv. 37, 30, 8: decem tria milia, id. 29, 2, 17; v. decem).