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Fifty-five is five times eleven and reduces to ten and then one. Its interest is chiefly mathematical: it is a triangular number, the sum of the integers one through ten, and it is a term in the Fibonacci sequence, the tenth, following thirty-four and preceding eighty-nine, one of the relatively few numbers that are both, which recreational mathematics notes with pleasure. The doubled five gives it, in numerological reading, an intensified quality of change and freedom before its reduction through ten to the unity of one.

Fifty-five falls outside Cheiro's original 1926 compound-number scheme, which stops at fifty-two, so no reading attributed to his book is reported here; Balliett's 1908 chart reduces it instead to one, by way of ten, initiative and new beginnings in the standard modern keyword list, a root shared with nineteen and thirty-seven and read, in the standard American chart, as the doubled five of change resolving into a single decisive direction. In chemistry, fifty-five is the atomic number of cesium, the element whose atomic vibrations define the modern second: the International System of Units has fixed the second, since 1967, as a specific count of oscillations of the cesium-133 atom, making this number's namesake element the literal basis of precise timekeeping worldwide.

Fifty-five carries no developed religious symbolism; the older traditions did not take it up, and its significance is confined to its arithmetical form and to the reductive readings of modern numerology, where the repeated five is sometimes treated as a heightened call to adventure and the senses. The honest account is a number whose whole interest lies in being at once triangular and Fibonacci, a coincidence of two of the more attractive number sequences, rather than in any body of tradition.

Walter Burkert's study of the Pythagorean tradition would treat fifty-five's status as both a triangular number and a Fibonacci term as a genuine mathematical property rather than a symbolic one, the sort of fact the ancient arithmological writers prized in numbers such as six and twenty-eight but did not, on his account, derive from Pythagoras himself; the coincidence of the two properties in one number is simply arithmetic, not evidence of any deliberate design by either the Fibonacci sequence's medieval discoverer or the ancient triangular-number tradition. The Fibonacci property noted above has a further consequence: the ratio of fifty-five to the Fibonacci number before it, thirty-four, is approximately zero point six one eight, an early approximation of the golden ratio, phi, which the ratio of consecutive Fibonacci numbers approaches ever more closely as the sequence grows.