Fzforty

Fzforty is equal to \(40^{40}\) = \(40\uparrow\uparrow2\) = 12,089,258,196,146,291,747,061,760,000,000,000,000,000,000,000,000,000,000,000,000,000

Etymology
Fzsixteen is made out of the Fz- prefix and forty, which ends up becoming \(40^{40}\) when concatenated backwards, ergo, 40 to the power of itself.