Like gray said, it depends on what you're trying to do, but if you're just trying to get a triangular prism to subdivide you might try something like this:
Left mesh: base mesh with supporting edge loops
Center mesh: base mesh with smooth preview
Right mesh: smoothed mesh with 2 divisions
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Left mesh: base mesh with supporting edge loops
Center mesh: base mesh with smooth preview
Right mesh: smoothed mesh with 2 divisions
look like origami made prism. Thank you very much.