Exinphi

Exinphi is equal to \(f_{\beta[10^{18}]}(10)\) using the fast-growing hierarchy; where \(\beta[n]\) defined as: The term was coined by wiki user Denis Maksudov.
 * \(\beta[0] = \omega\)
 * \(\beta[\alpha + 1] = \varphi(\beta[\alpha],0)\)