A hydrogen nucleus consists of a single proton. A 2-hydrogen (deuterium) nucleus consists of a proton and a neutron. A tritium nucleus consists of a proton and two neutrons.
This makes me wonder how an atomic nucleus made of a proton and a "minus one neutron" would look like, and the closest thing to a "minus one neutron" I can imagine is an antineutron.
What happens if we combine a proton and an antineutron? Are things like this even possible?
If such a thing is an atomic nucleus, can we add an electron and get an atom?
Edit: in the comments below, I also asked this more specific question (I suppose it's useful to also mention it here in order not to create a complete chaos):
If the proton and antineutron annihilate, is it still possible that the thing they annihilate to remains somehow stable enough to behave like an atomic nucleus?