What 21,196 km (13,171 mi) long feature has been built, dismantled, ignored, re-built, breached, abandoned and is currently serving mainly as a largely ruined tourist attraction?
Great Wall of China
The Great Wall of China is the collective name of a series of fortification and protection systems generally built across the historical northern borders of China. Some walls were being built in the 7th century BCE, of which little remains, The concept and the building was revived occasionally over the centuries, with the best known and best preserved walls being built by the Ming dynasty (13681644). Some of the later wall has been restored for tourist use, much of the rest has disappeared or is mostly ruined.
In mathematics, what is the name for the following sequence of numbers: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765 ...