Skewes'

e^ee79

≈ 10¹⁰¹⁰³⁴

Upper bound for first
π(x) > li(x) crossing

True value: unknown

Mills'

θ = A^3ⁿ

A ≈ 1.306377…

⌊A^3ⁿ⌋ is prime for all n
(assuming Riemann Hypothesis)

Exact value: unknown