55 (number)

← 54 55 56 →
← 50 51 52 53 54 55 56 57 58 59 → List of numbers — Integers ← 0 10 20 30 40 50 60 70 80 90 →
Cardinal	fifty-five
Ordinal	55th (fifty-fifth)
Factorization	5 × 11
Divisors	1, 5, 11, 55
Roman numeral	LV
Binary	1101112
Ternary	20013
Quaternary	3134
Quinary	2105
Senary	1316
Octal	678
Duodecimal	4712
Hexadecimal	3716
Vigesimal	2F20
Base 36	1J36

55 (fifty-five) is the natural number following 54 and preceding 56.

55 is the 10th Fibonacci number and a triangular number (the sum of the consecutive 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).

...
Wikipedia