Question

1+6+6^2+....+6^2018​

Answer 1

S = 1 + 6 + 6² + .. + 6²⁰¹⁸

6S = 6 + 6² + .. + 6²⁰¹⁹

6S = (1 + 6 + 6² + .. + 6²⁰¹⁸) + 6²⁰¹⁹ - 1

6S = S + 6²⁰¹⁹ - 1

6S - S = 6²⁰¹⁹ - 1

5S = 6²⁰¹⁹ - 1

S = (6²⁰¹⁹ - 1)/5