[tex]\frac{6+6^2+...+6^{98}+6^{99}+6^{100}}{1+2+4}=\\\\ \frac{6\cdot(1+6)+6^3\cdot(1+6)+...+6^{97}\cdot(1+6)+6^{99}\cdot(1+6)}{7}=\\\\\frac{6\cdot7+6^3\cdot7+...+6^{97}\cdot7+6^{99}\cdot7}{7}=\\\\\frac{7\cdot(6+6^3+...+6^{97}+6^{99})}{7}=6+6^3+...+6^{97}+6^{99}\in C[/tex]
