A single quintic vertex has five half-edges, so Wick theorem cannot contract all of them in pairs. The leading connected Vacuum Feynman diagrams therefore have two quintic vertices and are of order . If propagators join the two vertices, each vertex has half-edges left for tadpoles, so must be odd. This gives exactly three topologies:
The three diagrams are connected; every other pairing is either isomorphic to one of them or disconnected.
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