What is the next number in the series?

12 35 81 173 357 _______

Question

What is the next number in the series?

12   35   81   173   357   _______

Accepted Answer

725 Examining consecutive ratios and differences: 35 = 2*12 + 11, 81 = 2*35 + 11, 173 = 2*81 + 11, 357 = 2*173 + 11. Each term is double the previous plus 11. Alternatively, the consecutive differences are 23, 46, 92, 184 — each exactly double the previous difference. Either way, the next term is 2*357 + 11 = 725.