User blog comment:Wythagoras/Arrow notations/@comment-5029411-20140105190943

a ->-> a ->-> a has growth rate w^w

a ->-> a ->-> a -> 2 has growth rate w^w+1

a ->-> a ->-> a ->^ a has growth rate w^w+w^2

a ->->^ a has growth rate w^{w+1}

a ->->-> a has growth rate w^{w*2}