Natyashastra
एकैकं तु विदार्येका ते तु मद्विविधः स्मृतः । षट्परं त्र्यवरं वृत्तं द्व्यङ्गं सहरसं च तत् ॥ १८१॥
The Ekaka consists of one Vidārī, and the Vivadha of two and the Vṛtta not less than three and not more than six Vidārīs.
english translation
ekaikaM tu vidAryekA te tu madvividhaH smRtaH । SaTparaM tryavaraM vRttaM dvyaGgaM saharasaM ca tat ॥ 181॥
hk transliteration by Sanscript