4096^4096 ns: time taken by a 1GHz Turing machine (executing 1 instruction every 1ns) with 6 states to write all the 1s it can write, according to the Busy Beaver Problem. Busy Beaver problem: given a halting Turing machine, how many 1s can it write before halting? If the Turing machine in question has n states, this number is denoted S(n) and grows faster than any computable function f(n). If the Turing machine has 4 states, it writes 13 ones, if it has 5 states it writes at least 4098 ones (Buntrock-Marxen beaver, 1989), if it has 6 states it writes an enormous number of ones, not yet calculated but certainly > 4096^4096 (M.W. Green’s Theorem, 1964).
