Vivasvat drew his birth from Kaśyapa, and Manu from Vivasvat. Manu was formerly known as Prajāpati. Ikṣvāku is son to Manu; and this world was first conferred upon Ikşvāku by Manu. Do you know Ikşvāku as the first kind in Ayodhyā.
विवस्वान् कश्यपाज्जज्ञे मनुर्वैवस्वतः स्वयम्। स तु प्रजापतिः पूर्वमिक्ष्वाकुस्तु मनो सुतः॥ यस्येयं प्रथमं दत्ता समृद्धा मनुना मही। तमिक्ष्वाकुमयोध्यायां राजानं विद्धि पूर्वकम्॥