[tex]Notam\ x=\overline{a_1a_2a_3a_4a_5a_6}\\
\overline{3a_1a_2a_3a_4a_5a_6}=2\cdot \overline{a_1a_2a_3a_4a_5a_67}\\
3000000+\overline{a_1a_2a_3a_4a_5a_6}=2\cdot(10\cdot \overline{a_1a_2a_3a_4a_5a_6}+7)\\
3000000+x=2\cdot(10\cdot x+7)\\
3000000+x=20\cdot x+14\\
2999986=19x\\
x=157894=\overline{a_1a_2a_3a_4a_5a_6}\\
Verificare\\
3157894=2\cdot 1578947\\[/tex]