The main sequence lifetime for most main sequence stars is described by the following equation:

$$T=\frac{1}{M^{2.5}}$$

Note that this equation is in solar units. Mass M is in units of solar masses and Main Sequence Lifetime T is in units of solar lifetimes, where one solar lifetime is 10 billion years.

This equation is a rapidly decreasing function. As M grows, T decreases rapidly. This occurs because as mass increases this greatly increases temperature at the core of the star and the rate at which nuclear reactions occur. Massive stars use their nuclear fuel very rapidly and don't live very long. Low-mass stars use their fuel very conservatively and live a very long time.