$\zeta(5)$ is irrational.
$\zeta(7)$ is irrational.
$\zeta(9)$ is irrational.
$\zeta(11)$ is irrational.
theorem
RiemannZeta.irrational_odd
(n : ℕ)
(hn : 0 < n)
:
∃ (x : ℝ), Irrational x ∧ riemannZeta (2 * ↑n + 1) = ↑x
$\zeta(2n + 1)$ is irrational for any $n\in\mathbb{N}^{+}$.
$\zeta(3)$ is irrational.
[Ap79] Apéry, R. (1979). Irrationalité de ζ(2) et ζ(3). Astérisque. 61: 11–13.
There are infinitely many $\zeta(2n + 1)$, $n \in \mathbb{N}$, that are irrational.
[Ri00] Rivoal, T. (2000). La fonction zeta de Riemann prend une infinité de valeurs irrationnelles aux entiers impairs. Comptes Rendus de l'Académie des Sciences, Série I. 331 (4): 267–270.
At least one of $\zeta(5), \zeta(7), \zeta(9)$ or $\zeta(11)$ is irrational.
[Zu01] W. Zudilin (2001). One of the numbers ζ(5), ζ(7), ζ(9), ζ(11) is irrational. Russ. Math. Surv. 56 (4): 774–776.