No need to understand German to get this video.
Also: “Rüdiger Gamm (born July 10, 1971) is a German "mental calculator". He attained the ability to mentally evaluate large arithmetic expressions at the age of 21. He can also speak backwards, and calculate calendars. In the 2008 Mental Calculation World Cup in Leipzig, he recited 81100, which took approximately 2 minutes and 30 seconds. In the tournament itself, he performed strongly, finishing in 5th position overall.” - Wiki