Concerning π The second convergent of π, [3; 7] = 22/7 = 3.1428..., was known to Archimedes, and is correct to about 0.04%. The fourth convergent of π, [3; 7, 15, 1] = 355/113 = 3.1415929..., found by Zu Chongzhi, is correct to six decimal places; this high accuracy comes about because π has an unusually large next term in its continued fraction representation: = [3; 7, 15, 1, 292, ...]. A coincidence involving π and the golden ratio φ is given by . Consequently, the square on the middle-sized edge of a Kepler triangle is similar in perimeter to its circumcircle. Some believe one or the other of these coincidences is to be found in the Great Pyramid of Giza, but it is highly improbable that this was intentional. There is a sequence of six nines in pi, popularly known as the Feynman point, beginning at the 762nd decimal place of its decimal representation. For a randomly chosen normal number, the probability of a particular sequence of six consecutive digits—of any type, not just a repeating one—to appear this early is 0.08%. Pi is conjectured, but not known, to be a normal number. The first Feigenbaum constant is approximately equal to , with an error of 0.0015%. Concerning base 2 The coincidence , correct to 2.4%, relates to the rational approximation , or to within 0.3%. This relationship is used in engineering, for example to approximate a factor of two in power as 3 dB (actual is 3.0103 dB – see Half-power point), or to relate a kibibyte to a kilobyte; see binary prefix. This coincidence can also be expressed as (eliminating common factor of , so also correct to 2.4%), which corresponds to the rational approximation , or (also to within 0.3%). This is invoked for instance in shutter speed settings on cameras, as approximations to powers of two (128, 256, 512) in the sequence of speeds 125, 250, 500, etc, and in the original Who Wants to Be a Millionaire? game show in the question values ...£16,000, £32,000, £64,000, £125,000, £250,000,... Concerning musical intervals In music, the distances between notes (intervals) are measured as ratios of their frequencies, with near-rational ratios often sounding harmonious. In western twelve-tone equal temperament, the ratio between consecutive note frequencies is . The coincidence , from , closely relates the interval of 7 semitones in equal temperament to a perfect fifth of