$\qquad$ 1. A six-digit number $\overline{a b c d e f}$, when multiplied by 4, becomes $\overline{f a b c d e}$. The number of six-digit numbers that satisfy this condition is $\qquad$.
$=1.6$
Let $\overline{a b c d e}=x$. Then
$$
\begin{array}{l}
4(10 x+f)=100000 f+x \\
\Rightarrow x=2564 f .
\end{array}
$$

Since $f$ is a single digit and $x$ is a five-digit number, it is easy to see that,
$$
f=4,5,6,7,8,9 \text {. }
$$

Therefore, the six-digit numbers $\overline{a b c d e f}$ that satisfy the condition are
$$
\begin{array}{l}
102564,128205,153846, \\
179487,205128,230769,
\end{array}
$$

a total of 6.