Look at your atomic masses for phosphorus and oxygen. Set up 2.5/31 and 3.23/16. This makes 0.08 and 0.2. Now consider 0.08/0.2 to equal 0.4. So, your ratio of P to O is 0.4, which is 4/10. So, your formula, which reflects that ratio, is P4O10. That's tetraphosphorus decoxide, a molecular solid used in match-heads.
This compound may be dioxane - C4H8O2.
the answer is: P4O10