Can antineutrons combine with (regular ol') protons to form a not-quite-hydrogen nucleus? Is it possible that many of the neutrons out there are antineutrons?

I don't know the math, I don't know the particle physics, but part of me has to wonder if the baryonic assymetry is a result of positrons and antiprotons combining at a significantly higher rate than the electron-proton (due to a minor asymmetry we might not have measured yet). That would take most of the antimatter "out" of the universe as antineutrons -- and some of that matter might be "dark" too, right?