555 (number)

This article is about the integer. For the telephone number, see 555 (telephone number). For other uses, see 555 (disambiguation).

← 554 555 556 →
List of numbers Integers ← 0 100 200 300 400 500 600 700 800 900 →
Cardinal	five hundred fifty-five
Ordinal	555th (five hundred fifty-fifth)
Factorization	3 × 5 × 37
Divisors	1, 3, 5, 15, 37, 111, 185, 555
Greek numeral	ΦΝΕ´
Roman numeral	DLV, dlv
Binary	10001010112
Ternary	2021203
Senary	23236
Octal	10538
Duodecimal	3A312
Hexadecimal	22B16

555 (five hundred [and] fifty-five) is the natural number following 554 and preceding 556.

In mathematics

555 is a sphenic number, with prime factorization 3 × 5 × 37. ^[1] In base 10, it is a repdigit, and because it is divisible by the sum of its digits (15), it is a Harshad number. It is also a Harshad number in binary, base 11, base 13 and hexadecimal.

555 is also a Moran number, because 555 ÷ (5+5+5) = 555 ÷ 15 = 37, and 37 is prime. ^[1]

It is the sum of the first triplet of three-digit permutable primes in decimal:

${\displaystyle 113+131+311=555}$.

It is the twenty-sixth number such that its Euler totient (288) is equal to the totient value of its sum-of-divisors: ${\displaystyle \varphi (555)=\varphi (\sigma (555))}$. ^[2]

In technology

The 555 timer IC is an integrated circuit used in timer, delay, pulse generation, and oscillator applications. Designed in 1971 by Hans Camenzind for Signetics, it was first marketed in 1972 and became one of the most popular integrated circuits ever produced, with over a billion units manufactured annually. ^[3]

In North American telephone numbering, the 555 prefix is reserved for directory assistance and fictional use. Numbers in the range 555-0100 through 555-0199 are specifically set aside for use in fiction, allowing films and television shows to display phone numbers without risking calls to real subscribers. ^[4]

In astronomy

555 Norma is a main-belt asteroid discovered at the Heidelberg Observatory. It was named after the title character of the opera Norma by Italian composer Vincenzo Bellini. ^[5]

NGC 555 is a lenticular galaxy located approximately 479 million light-years away in the constellation Cetus. It was discovered in 1886 by American astronomer Frank Muller. ^[6]

Year

Year 555 saw the Byzantine Empire under Justinian I reach its greatest territorial extent, having reconquered Italy, Dalmatia, Africa, and southern Hispania. ^[7] On June 7 of that year, Pope Vigilius died at Syracuse while returning to Rome. ^[8]

References

1. "Properties of number 555". www.numbersaplenty.com. Archived from the original on 2024-12-06. Retrieved 2025-04-03. It is a Harshad number since it is a multiple of its sum of digits (15), and also a Moran number because the ratio is a prime number: 37 = 555 / (5 + 5 + 5).
2. Sloane, N. J. A. (ed.). "SequenceA006872(Numbers k such that phi(k) is phi(sigma(k)).)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved 2023-08-31.
3. "555 Timer Tutorial". Electronics Tutorials. Retrieved 2026-01-26.
4. "What Are 555 Phone Numbers?". Federal Communications Commission. Retrieved 2026-01-26.
5. "555 Norma". JPL Small-Body Database. NASA. Retrieved 2026-01-26.
6. "NGC 555". The NGC/IC Project. Retrieved 2026-01-26.
7. "555". Encyclopaedia Britannica. Retrieved 2026-01-26.
8. "Pope Vigilius". Catholic Encyclopedia. Retrieved 2026-01-26.

External links

• Media related to 555 (number) at Wikimedia Commons