Number reference
555 explained.
555: five hundred fifty-five, composite, repdigit; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- five hundred fifty-five
- Classification
- composite
- Factors
- 1, 3, 5, 15, 37, 111, 185, 555
- Prime factorization
- 3 × 5 × 37
- Square root
- 23.558438
- Cube root
- 8.217966
- Binary
- 1000101011
- Octal
- 1053
- Hexadecimal
- 22B
- Roman numeral
- DLV
- Digit sum
- 15
- Digital root
- 6
What makes 555 notable
- Repdigit. 555 is written with a single repeated digit, so it is divisible by the repunit of the same length.
555 in everyday use
Five hundred fifty-five is the prefix of telephone numbers that do not exist. North American films and television use 555 numbers so that viewers cannot dial a real household, and the range 555-0100 to 555-0199 is officially reserved for fiction. Electronics hobbyists know it as the 555 timer, an integrated circuit designed by Hans Camenzind and released in 1972 that produces pulses and delays; it is still made in the billions and is often the first chip a beginner wires up.
The number is a repdigit and factors as 3 × 5 × 37, three distinct primes, which makes it sphenic with eight divisors. Like all three-digit repdigits it is a multiple of 111, and 555 ÷ 37 = 15. It is 1000101011 in binary and 22B in hexadecimal. Its digit sum is 15, which divides it, so it is a Harshad number, and it lies between the primes 547 and 557.
Nearby numbers
How to read this page
The factor list shows every way 555 splits into equal whole-number groups — 8 divisors in total. The prime factorisation is the compact form of that same information, and the base conversions restate 555 for contexts that do not use decimal.
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