How to calculate Edit
let's imagine number i0
i0 is pretty small, i0 = 2^2
not so large
i0 = 4
i1 = i0^i0^i0^i0 = 4^4^4^4 (4^ repeated 4 times) = 340282366920938463463374607431768211456
not so small, isn't it?
i2 = i1^i1^i1^i1^i1....... (i1 times in total)
it's extremely large
even i2 is incalculable
i3 = i2^i2^i2........ (i2 times)
i42 = Killbots number
it is so large, that it possibly larger that Grahams Number
both numbers are incalculable, so, we won't ever know.