Gex is the name for the one-argument Ackermann function, A(10), a contraction of the two-argument function, A(10, 10), a contraction of the three-argument function, g(11, 10, 10) = g(12, 2, 10), ten-dodecated-to-the-second, with a verbalized -x-, so as not to be confused with Joyce's gox aka giji.
It is equal to tridecal.
Gex is also the name of a game for the 3D0, in which a character purportedly yells "Meameamealokkapoowa," providing that number's name.