The Great Pyramid having eight sides was most recently referenced in a 2023 study for the Archaeological Discovery journal.

the Taj Mahal and the Great Pyramid, to reveal the hidden geometry at their cores. At each iconic structure he examines a fundamental form: at Stonehenge - the circle: the Taj Mahal - the square ...

If you guessed five or three you are also incorrect and maybe a little confused about geometry ... the Great Pyramid is a concave octagonal pyramid, rather than the standard square pyramid.