Nine of the remaining sons of Ṛṣabhadeva became the rulers of the nine islands of Bhārata-varṣa, and they exercised complete sovereignty over this planet. Eighty-one sons became twice-born brāhmaṇas and helped initiate the Vedic path of fruitive sacrifices [karma-kāṇḍa].
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
तेषां नव नवद्वीपपतयोऽस्य समन्ततः । कर्मतन्त्रप्रणेतार एकाशीतिर्द्विजातयः
teṣāṃ nava navadvīpapatayo'sya samantataḥ | karmatantrapraṇetāra ekāśītirdvijātayaḥ
SB 11.2.19