Rasa2 ( -- ˚) is a dial. form of ˚dasa ten, and occurs in Classic Pāli only in the numerals for 13 (terasa), 15 (paṇṇa -- rasa, pannarasa), 17 (sattarasa) & 18 (aṭṭhārasa, late). The Prk. has gone further: see Pischel, Prk. Gr. § 245.