śateka vatsara haya - there are one hundred years; jīvana - the duration of life; brahmāra - of Brahmā; pañca-lakṣa - 500,000; cāri-sahasra - 4,000; manu-antara-avatāra - incarnations who appear during the reign of each Manu.

“During the hundred years of Brahmā’s life, there are 504,000 manvantara-avatāras.