$$2MG/c^2$$
The Bondi radius is $$2MG/s^2$$ where M is the mass, G is the gravitational constant and $$s$$ is the speed of sound in the medium of the accretion disk. It represents the boundary between sub-sonic and super-sonic infall of matter into the black hole.
The Schwartzchild radius is $$2MG/c^2$$ where $$c$$ is the speed of light and is the radius of the event horizon.
• The OP's error possibly derives from the Wikipedia page, which gives the denominator in the expression as $c_{s}^{2}$ where $c_{s}$ is defined as the sound speed in the surrounding medium. A good lesson in paying attention to subscripts ;-) – Chappo Jan 2 at 0:39