I am a hermit, so I am usually a party of one. I don't like having people over, and don't really like going out much. I do occasionally visit nearby relatives, or go out to eat with them, but that's about it. Being a hermit, I don't have friends, so there is no one to go out with anyway.
As for your situation, just invite them, and either they will say yes, or no. If you want them over at your place, you could have a theme party, or have some sort of special meal prepared, that you should mention in your invite. If this is to be an outside event, pick something you think they will like, and again, mention that in the invite. It could be as simple as a favorite restaurant, or new movie, or something more involved, like attending a concert by a group they like, or a sporting event they like, etc., and don't forget to mention that in the invite.
Hope this helps. 
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If a man does not keep pace with his companions, perhaps it is because he hears a different drummer.
Let him step to the music which he hears, however measured, or far away.--Henry David Thoreau