what is the half-life equation for a muon (unstable particle that spontaniously decays)?

According to this site (http://www.lbl.gov/abc/cosmic/SKliewer/Cosmic_Rays/Muons.htm), muons have a half life of 2.2\mu s

The equation therefore is Initial\, mass\, of \,muon \times\( \frac12 \)^{2.2n}

Where 'n' is the number of '2.2' micro second which has passed from the start of the decomposition process.