255 (number)

← 254 256 → 255
← 200 210 220 230 240 250 260 270 280 290 → List of numbers — Integers ← 0 100 200 300 400 500 600 700 800 900 →
Cardinal	Two hundred [and] fifty-five
Ordinal	255th (Two hundred [and] fifty-fifth)
Factorization	$255 = 3 \cdot 5 \cdot 17$
Roman numeral	CCLV
Binary	11111111₂
Octal	377₈
Duodecimal	193₁₂
Hexadecimal	FF₁₆

255 (two hundred [and] fifty-five, CCLV) is the natural number following 254 and preceding 256.

In mathematics

Its factorization makes it a sphenic number. Since 255 = 2⁸ - 1, it is a Mersenne number, and the fourth such number not to be a prime number. It is a perfect totient number, the smallest such number to be neither a power of three nor thrice a prime.

In base 10, it is a self number.

255 is a repdigit in base 2 (11111111) in base 4 (3333), and in base 16 (FF).

In computing

255 is a special number in some tasks having to do with computing. This is the maximum value representable by an eight-digit binary number, and therefore the maximum representable by an unsigned 8-bit byte (the most common size of byte, also called an octet), the smallest common variable size used in high level programming languages (bit being smaller, but rarely used for value storage). The range is 0 to 255, which is 256 total values.

$255 = 2^8 - 1 = \mbox{FF}_{16} = 11111111_2$

For example, 255 is the maximum value

that can be assigned to elements in the 24-bit RGB color model, since each color channel is allotted eight bits.
of any dotted quad in an IP address.
of the alpha blending scale in Delphi (255 being 100% visible and 0 being fully transparent)

The use of eight bits for storage in older video games has had the consequence of it appearing as a hard limit in many video games. In the earlier versions of The Legend of Zelda, Link can carry a maximum of 255 rupees.^[1] It was often used for numbers where casual gameplay would not cause anyone to exceed the number. However, in most situations it is reachable given enough time. This can cause many other peculiarities to appear when the number wraps back to 0.

This number could be interpreted by a computer as −1 if a programmer is not careful about which 8-bit values are signed and unsigned, and the two's complement representation of −1 in a signed byte is equal to that of 255 in an unsigned byte.

References

^ Hoovler, Evan. "The History of Annoying Side-Quests in Videogames." GameSpy. 2009-12-04.