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
Greek numeral	ΝΕ´
Roman numeral	LV, lv
Binary	1101112
Ternary	20013
Senary	1316
Octal	678
Duodecimal	4712
Hexadecimal	3716

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

Mathematics

55 is a square pyramidal number.

55 is:

• the 10th Fibonacci number and the 10th triangular number, The sum of 55's digits is also 10.
• the 5th heptagonal number, the 5th square pyramidal number, and the 4th centered nonagonal number.

55 is also the 19th semiprime and the 15th squarefree semiprime, as well as the 32nd nontotient number (including odd numbers > 1) the 36th arithmetic number, the 38th composite number (where the abundance of 55 = - 38), the 43rd deficient number, the 45th trapezoidal number, and the 49th polite number.

Transportation

• In the United States, the National Maximum Speed Law prohibited speed limits higher than 55 miles per hour (90 km/h) from 1974 to 1987. The number 55 became a popular shorthand for the 55 mph speed limit. For example, a hand with a pair of fives in Texas hold'em poker is referred to as a "speed limit".