Hadar Zekenim (on Pasuk 13): The Siman is 'ABaD Izim' - The Torah writes 'Se'ir Izim' on days 'Alef,' 'Beis' and 'Dalet'. Yisrael are Azim (most brazen) of the nations. These days are the order in which our Avos was born ? Avraham was first, Yitzchak second, and Ya'akov fourth. Eisav was third (and he is called Se'ir)!

R. Bachye (Vayikra 1:5): Se'ir Stam is a yearling. Se'ir Izim is above one year.

Rosh (on 28:9): It says "Se'ir Izim" on days one, two and four. The total number of bulls offered on those days is thirty-five, the same as the days that it says "Se'ir".

Kol Eliyahu and Divrei Eliyahu citing the Zohar: Refer to answer #3. Thirty-five nations nurture from Yishmael, who is called 'Se'ir Izim', and thirty-five from Eisav, who is called 'Se'ir'..