Pāṇini sūtras

The affix ḍa comes in the sense of “this is surplus in it”, after a Numeral ending in śat and after viṁśati; with the elision of at and ati

1. śat+anta+viṃśateḥशत्+अन्त+विंशतेः

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   śश्	śatशत्	śatशत्	śatशत्	śatशत्
   aअ	antaअन्त	antaअन्त	end	antअन्त् + plus aअ
   vव्	viṃśatiविंशति	viṃśateḥविंशतेः	viṃśati [word]विंशति [wओर्द्]	viṃśatविंशत् + plus eḥएः

2. caच

   Part	Lexeme	Sandhi form	Meaning	Stem
   cच्	caच	caच	besides	caच

Anuvṛtti

1. adhikamअधिकम् 5·2·45

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	adhikaअधिक	adhikamअधिकम्	more(a)	adhikअधिक् + plus amअम्