What is the current flowing through the resistor in this circuit?
\$R1\$, \$R2\$ and \$R4\$ are not in parallel, they are connected in a star or T configuration.
The current \$I_0\$ is devided between \$R_1\$ and \$R_{346}\$ in the first part of circuit, where \$R_{346}=R_3+R_4+R_6\$.
From the basic current divider formula:
$$I_{346}=\frac{R1}{R1+R_{346}}I_0$$