Not a Number

Not a Number is the third track included in the first disc of the Halo 2: Anniversary Original Soundtrack. It is the remastered orchestral version of Remembrance from the Halo 2: Original Soundtrack, while Unsullied Memory is the remastered vocal version.

Halo: The Master Chief Collection
Not a Number is one of the tracks featured in the menus of Halo: The Master Chief Collection. The menu music opens with the monk chant from the Combat Evolved Anniversary OST track Installation 04, followed by Not a Number and ending with the Halo 2: Anniversary track Unwearied Heart.