Here are 20 important unsolved problems in mathematics:

1. Riemann Hypothesis
2. Birch and Swinnerton-Dyer Conjecture
3. Hodge Conjecture
4. P versus NP
5. Yang-Mills Existence and Mass Gap
6. Navier-Stokes Equation
7. Existence of a Solution for the Neumann Problem in Three Dimensions
8. Bounded Gaps Conjecture for Prime Numbers
9. Twin Prime Conjecture
10. Goldbach Conjecture
11. Collatz Conjecture
12. Hadamard Conjecture
13. Euler's Conjecture on Sums of Powers
14. Fermat's Last Theorem for higher exponents
15. Baum–Connes Conjecture
16. Oppenheim Conjecture
17. The Continuum Hypothesis
18. Novikov Conjecture
19. The Hirsch Conjecture
20. Schanuel's Conjecture


Please note that while there are many unsolved problems in mathematics, it is difficult to determine a definitive list of the top 20 most important ones as importance can be subjective and can vary depending on the field of mathematics. However, you may find more information on various unsolved problems in mathematics on the Wikipedia page “List of unsolved problems in mathematics”.
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