Number

123

123 is a composite number, odd, a calendar year.

123 (one hundred twenty-three) is an odd 3-digit number. It is a composite number with 4 divisors, and factors as 3 × 41. It is a Lucas number. Written other ways, in Roman numerals it is CXXIII and in binary, 1111011.

Arithmetic Number Ascending Digits Consecutive Digits Cube-Free Deficient Number Evil Number Lucas Recamán's Sequence Semiprime Squarefree Year

Interestingness

★ ★ ★ ★ ★

8 notable facts · grade A

111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135

less more

Historical context — 123 AD

Calendar year

Year 123 (CXXIII) was a common year starting on Thursday of the Julian calendar.

Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 Read the full article on Wikipedia →

Historical context — 123 BC

Calendar year

Year 123 BC was a year of the pre-Julian Roman calendar.

Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 Read the full article on Wikipedia →

Year facts

Year type: Common year
Standard 365-day year; not divisible by 4 (or divisible by 100 but not 400).
Days in year: 365
ISO weeks: 52
Started on: Friday
January 1, 123
Ended on: Friday
December 31, 123
Friday the 13ths: 1
One Friday the 13th this year.
Decade: 120s
120–129
Century: 2nd century
101–200
Millennium: 1st millennium
1–1000
Years ago: 1,903
1903 years before 2026.

In other calendars

Hebrew: 3883 / 3884 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Water zodiac:Pig
Sexagenary cycle position 60 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 666 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: 115 / 116 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 45 / 44 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 3
Digit sum: 6
Digit product: 6
Digital root: 6
Palindrome: No
Bit width: 7 bits
Reversed: 321
Recamán's sequence: a(154) = 123
Square (n²): 15,129
Cube (n³): 1,860,867
Divisor count: 4
σ(n) — sum of divisors: 168
φ(n) — Euler's totient: 80
Sum of prime factors: 44

Primality

Prime factorization: 3 × 41

Nearest primes: 113 (−10) · 127 (+4)

Divisors & multiples

All divisors (4)

1 · 3 · 41 · 123

Aliquot sum (sum of proper divisors): 45

Factor pairs (a × b = 123)

1 × 123

3 × 41

First multiples

123 · 246 (double) · 369 · 492 · 615 · 738 · 861 · 984 · 1,107 · 1,230

Sums & aliquot sequence

As consecutive integers: 61 + 62 40 + 41 + 42 18 + 19 + 20 + 21 + 22 + 23

Aliquot sequence: 123 → 45 → 33 → 15 → 9 → 4 → 3 → 1 → 0 — terminates at zero

Continued fraction of √n

√123 = [11; (11, 22)]

Period length 2 — the block in parentheses repeats forever.

Representations

In words: one hundred twenty-three
Ordinal: 123rd
Roman numeral: CXXIII
Binary: 1111011
Octal: 173
Hexadecimal: 0x7B
Base64: ew==
One's complement: 132 (8-bit)
Scientific notation: 1.23 × 10²
As a duration: 123 s = 2 minutes, 3 seconds

In other bases

ternary (3) 11120

quaternary (4) 1323

quinary (5) 443

senary (6) 323

septenary (7) 234

nonary (9) 146

undecimal (11) 102

duodecimal (12) a3

tridecimal (13) 96

tetradecimal (14) 8b

pentadecimal (15) 83

Palindromic in base 6

As an angle

123°

123° ≈ 2.147 rad

Compass bearing: ESE (east-southeast)

Why does a circle have 360 degrees? →

Historical numeral systems

Babylonian (base 60): 𒁹𒁹 𒁹𒁹𒁹
Egyptian hieroglyphic: 𓍢𓎆𓎆𓏺𓏺𓏺
Greek (Milesian): ρκγʹ
Mayan (base 20): 𝋦·𝋣
Chinese: 一百二十三
Chinese (financial): 壹佰貳拾參

In other modern scripts

Eastern Arabic ١٢٣ Devanagari १२३ Bengali ১২৩ Tamil ௧௨௩ Thai ๑๒๓ Tibetan ༡༢༣ Khmer ១២៣ Lao ໑໒໓ Burmese ၁၂၃

Digit at this position in famous constants

π — Pi (π): Digit 123 = 9
e — Euler's number (e): Digit 123 = 1
φ — Golden ratio (φ): Digit 123 = 2
√2 — Pythagoras's (√2): Digit 123 = 2
ln 2 — Natural log of 2: Digit 123 = 8
γ — Euler-Mascheroni (γ): Digit 123 = 6

Also seen as

ASCII character

As an ASCII codepoint, 123 is {. Printable ASCII character {.

Network port

TCP/UDP port 123 is the well-known port for NTP — Network Time Protocol.

Hex color

#00007B

RGB(0, 0, 123)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.123.

Address: 0.0.0.123
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.0.123

Unspecified address (0.0.0.0/8) — "this network" placeholder.

Musical pitch

Heard as a frequency, 123 Hz is closest to:

Concert pitch (A4 = 440 Hz): B2 (123.5 Hz, -7¢)
Scientific pitch (C4 = 256 Hz): B2 (120.8 Hz, +31¢)
Baroque pitch (A4 = 415 Hz): C3 (123.4 Hz, -5¢)

As a MIDI note number, 123 is D♯9 (9956.1 Hz at concert pitch).