data/problems/188.yml
---
:id: 188
:name: The hyperexponentiation of a number
:url: https://projecteuler.net/problem=188
:content: "The hyperexponentiation or tetration of a number a by a positive integer
b, denoted by a↑↑b or <sup>b</sup>a, is recursively defined by: \n \na↑↑1 = a,
\ \na↑↑(k+1) = a<sup>(a↑↑k)</sup>.\n\nThus we have e.g. 3↑↑2 = 3<sup>3</sup> = 27,
hence 3↑↑3 = 3<sup>27</sup> = 7625597484987 and 3↑↑4 is roughly 10<sup>3.6383346400240996*10^12</sup>.\n\nFind
the last 8 digits of 1777↑↑1855.\n\n"