555 (number)

In mathematics

555 is a sphenic number, with prime factorization 3 × 5 × 37. 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.

It is the sum of the first triplet of three-digit permutable primes in decimal: :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: \varphi(555) = \varphi(\sigma(555)).

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.

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.

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.

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.

Year

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

References

References

1. "Properties of number 555".
2. {{Cite OEIS. A006872. Numbers k such that phi(k) is phi(sigma(k)).
3. "555 Timer Tutorial".
4. "What Are 555 Phone Numbers?".
5. "555 Norma". NASA.
6. "NGC 555".
7. "555".
8. "Pope Vigilius".