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55 (number)
55 (fifty-five) is the natural number following 54 and preceding 56. ==Mathematics== 55 is the 10th Fibonacci number and a triangular number (the sum of the numbers 1 to 10). It is the largest Fibonacci number to also be a triangular number. It is a square pyramidal number (the sum of the squares of the integers 1 to 5) as well as a heptagonal number, and a centered nonagonal number. In base 10, it is a Kaprekar number. 55 is a semiprime, being the product of 5 and 11 and it is the 2nd member of the (5.q) semiprime family. 55 is one of only two integers with an aliquot sum of 17 (the other being 39). 55 has an aliquot sequence of 4 members: (55, 17, 1, 0). 55 is also the sum of consecutive numbers from 1 to 10.
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