# Problem 188: The hyperexponentiation of a number
The hyperexponentiation or tetration of a number a by a positive integer
b, denoted by a↑↑b or ba, is recursively defined by: a↑↑1 = a, a↑↑(k+1)
= a(a↑↑k). Thus we have e.g. 3↑↑2 = 33 = 27, hence 3↑↑3 = 327 =
7625597484987 and 3↑↑4 is roughly 103.6383346400240996\*10\^12. Find the
last 8 digits of 1777↑↑1855.