In mathematics, Mahler's 3/2 problem concerns the existence of "Z-numbers".

A Z-number is a real number x such that the fractional parts of

${\displaystyle x\left({\frac {3}{2}}\right)^{n}}$

are less than 1/2 for all positive integers n. Kurt Mahler conjectured in 1968 that there are no Z-numbers.

More generally, for a real number α, define Ω(α) as

${\displaystyle \Omega (\alpha )=\inf _{\theta >0}\left({\limsup _{n\rightarrow \infty }\left\lbrace {\theta \alpha ^{n}}\right\rbrace -\liminf _{n\rightarrow \infty }\left\lbrace {\theta \alpha ^{n}}\right\rbrace }\right).}$

Mahler's conjecture would thus imply that Ω(3/2) exceeds 1/2. Flatto, Lagarias, and Pollington showed^[1] that

${\displaystyle \Omega \left({\frac {p}{q}}\right)>{\frac {1}{p}}}$

for rational p/q > 1 in lowest terms.