Given positive integers
and
,
we write
for the integer
whose base-
representation is the concatenation
of the base-
representations of
.
In this paper, we prove that if
is
a binary recurrent sequence of integers satisfying some mild
hypotheses, then for every fixed integer
,
there are at most finitely many nonnegative integers
such that
is
a member of the sequence
. In particular,
we compute all such instances in the special case that
,
,
and
is the sequence of Fibonacci numbers.