Erd\H os and R\'{e}nyi claimed and Vu proved that for all $h \ge 2$ and for
all $\epsilon > 0$, there exists $g = g_h(\epsilon)$ and a sequence of integers
$A$ such that the number of ordered representations of any number as a sum of
$h$ elements of $A$ is bounded by $g$, and such that $|A \cap [1,x]| \gg x^{1/h
- \epsilon}$.
We give asymptotic sharp estimates for the cardinality of a set of residue
classes with the property that the representation function is bounded by a
prescribed number. We then use this to obtain an analogous result for sets of
integers, answering an old question of Simon Sidon.
We give a slight improvement of the best known lower bound for the supremum
of autoconvolutions of nonnegative functions supported in a compact interval.
Also, by means of explicit examples we disprove a long standing natural
conjecture of Schinzel and Schmidt concerning the extremal function for such
autoconvolutions.
We give a slight improvement of the best known lower bound for the supremum
of autoconvolutions of nonnegative functions supported in a compact interval.
Also, by means of explicit examples we disprove a long standing natural
conjecture of Schinzel and Schmidt concerning the extremal function for such
autoconvolutions.