DISPROVED
This has been solved in the negative.
Let $A(x)$ count the number of $n\leq x$ which are the sum of two squarefull numbers (a number $m$ is squarefull if $p\mid m$ implies $p^2\mid m$). Is it true that\[A(x) \sim c \frac{x}{\sqrt{\log x}}\]for some $c>0$?
Odoni
[Od81] proved this is false, and that\[A(x) \gg \exp\left(c\frac{\log\log\log x}{\log\log x}\right)\frac{x}{\sqrt{\log x}}\]for some constant $c>0$. Estimates for $A(x)$ have been improved by Baker and Brudern
[BaBr94], Blomer
[Bl04], and most recently by Blomer and Granville
[BlGr06], who proved\[A(x)= (\log\log x)^{O(1)}\frac{x}{(\log x)^{\alpha}}\]where $\alpha=1-2^{-1/3}\approx 0.206299$.
See also
[940].
View the LaTeX source
This page was last edited 15 October 2025.
Additional thanks to: Alfaiz and epistemologist
When referring to this problem, please use the original sources of Erdős. If you wish to acknowledge this website, the recommended citation format is:
T. F. Bloom, Erdős Problem #1081, https://www.erdosproblems.com/1081, accessed 2026-01-16