Many of these spirals exhibit a rate of expansion that correlates with the Fibonacci sequence, a mathematically significant group of numbers in which each is the sum of the preceding two (0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55). Dividing successive Fibonacci numbers yields a ratio known as the golden mean (approximately 1.61803), which some historians believe was used by the ancient Egyptians in the design of the Pyramids at Giza and by the ancient Greeks in the Parthenon.
