sańkhyānaḿ yādavānāḿ kaḥ
kariṣyati mahātmanām
yatrāyutānām ayuta-
lakṣeṇāste sa āhukaḥ
sankhyanam -- the counting; yadavanam -- of the Yadavas; kah -- who; karishyati -- can do; maha-atmanam -- of the great personalities; yatra -- among whom; ayutanam -- of tens of thousands; ayuta -- (times) ten thousand; lakshena -- with (three) hundred thousand (persons); aste -- was present; sah -- he; ahukah -- Ugrasena.
Srila Visvanatha Cakravarti explains why specifically thirty trillion, rather than an indefinite number of tens of trillions, is stated here to be the number of King Ugrasena's attendants. He does so by citing the interpretational rule of kapinjaladhikarana, the logic of "referring to pigeons": Somewhere in the Vedas is found the injunction that "one should sacrifice some pigeons." This plural number should be taken to mean not an indiscriminate number of pigeons, but precisely three of them, since the Vedas never leave any matter vague. The rules of Mimamsa interpretation take three as the default number when no specific number is given.