Calculating the 13th root of a large number (that is a perfect 13th power) is a famous mental calculation challenge. However, because of difficulties in standardizing the time taken to find the root, the Guinness Book of World Records no longer maintains an entry for the 13th root.
The official record (as of August 2005) is 13.55 seconds for a 100-digit perfect 13th power, as calculated by Alexis Lemaire on May 10, 2002. (By comparison, the Wolfram Language computes such roots in about 51 microseconds.) The record for a 200-digit number was also set by Lemaire, at 267.77 seconds (whereas the Wolfram Language takes roughly 82 microseconds).
