The affix tayap comes in the sense of 'that whereof the parts are so many' after a numeral.,
The word तदस्य is understood here. Thus पंच अवयवा अस्य = पंचतयम् 'having five parts'. The part being connected with the whole, the force of the affix is to denote the whole. So also दशतयम्, चतुष्टयम्, चतुष्टयी 8.3.101 and 4.5.15,