Clarify.
diff --git a/Doc/tutorial/datastructures.rst b/Doc/tutorial/datastructures.rst
index cbf3491..226eadd 100644
--- a/Doc/tutorial/datastructures.rst
+++ b/Doc/tutorial/datastructures.rst
@@ -170,7 +170,8 @@
``filter(function, sequence)`` returns a sequence consisting of those items from
the sequence for which ``function(item)`` is true. If *sequence* is a
:class:`string` or :class:`tuple`, the result will be of the same type;
-otherwise, it is always a :class:`list`. For example, to compute some primes::
+otherwise, it is always a :class:`list`. For example, to compute primes up
+to 25::
>>> def f(x): return x % 2 != 0 and x % 3 != 0
...