Number

19

19 is a prime, odd, a calendar year.

Arithmetic Number Centered Hexagonal Centered Triangular Chen Prime Cousin Prime Cuban Prime Cube-Free Deficient Number Flippable Happy Number Keith Number Octahedral Number Odious Number Pernicious Number Prime Recamán's Sequence Sexy Prime Squarefree Twin Prime Year

Historical context — 19 AD

Calendar year

AD 19 (XIX) was a common year starting on Sunday of the Julian calendar.

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Historical context — 19 BC

Calendar year

Year 19 BC was either a common year starting on Thursday, Friday or Saturday or a leap year starting on Thursday or Friday of the Julian calendar and a common year starting on Wednesday of the Proleptic Julian calendar.

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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: Tuesday
January 1, 19
Ended on: Tuesday
December 31, 19
Friday the 13ths: 2
2 Friday the 13ths this year.
Decade: 10s
10–19
Century: 1st century
1–100
Millennium: 1st millennium
1–1000
Years ago: 2,007
2007 years before 2026.

In other calendars

Hebrew: 3779 / 3780 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Earth zodiac:Rabbit
Sexagenary cycle position 16 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 562 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: 11 / 12 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): -59 / -60 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 2
Digit sum: 10
Digit product: 9
Digital root: 1
Palindrome: No
Bit width: 5 bits
Reversed: 91
Flips to (rotate 180°): 61
Recamán's sequence: a(99,734) = 19
Square (n²): 361
Cube (n³): 6,859
Divisor count: 2
σ(n) — sum of divisors: 20
φ(n) — Euler's totient: 18

Primality

19 is prime. It has exactly two divisors: 1 and itself.

Divisors & multiples

All divisors (2)

1 · 19

Aliquot sum (sum of proper divisors): 1

Factor pairs (a × b = 19)

1 × 19

First multiples

19 · 38 (double) · 57 · 76 · 95 · 114 · 133 · 152 · 171 · 190

Sums & aliquot sequence

As consecutive integers: 9 + 10

Continued fraction of √n

√19 = [4; (2, 1, 3, 1, 2, 8)]

Period length 6 — the block in parentheses repeats forever.

Representations

In words: nineteen
Ordinal: 19th
Roman numeral: XIX
Binary: 10011
Octal: 23
Hexadecimal: 0x13
Base64: Ew==
One's complement: 236 (8-bit)
Scientific notation: 1.9 × 10¹

In other bases

ternary (3) 201

quaternary (4) 103

quinary (5) 34

senary (6) 31

septenary (7) 25

nonary (9) 21

undecimal (11) 18

duodecimal (12) 17

tridecimal (13) 16

tetradecimal (14) 15

pentadecimal (15) 14

Historical numeral systems

Babylonian (base 60): 𒌋𒁹𒁹𒁹𒁹𒁹𒁹𒁹𒁹𒁹
Egyptian hieroglyphic: 𓎆𓏺𓏺𓏺𓏺𓏺𓏺𓏺𓏺𓏺
Greek (Milesian): ιθʹ
Mayan (base 20): 𝋳
Chinese: 一十九
Chinese (financial): 壹拾玖

In other modern scripts

Eastern Arabic ١٩ Devanagari १९ Bengali ১৯ Tamil ௧௯ Thai ๑๙ Tibetan ༡༩ Khmer ១៩ Lao ໑໙ Burmese ၁၉

Digit at this position in famous constants

π — Pi (π): Digit 19 = 8
e — Euler's number (e): Digit 19 = 5
φ — Golden ratio (φ): Digit 19 = 8
√2 — Pythagoras's (√2): Digit 19 = 8
ln 2 — Natural log of 2: Digit 19 = 9
γ — Euler-Mascheroni (γ): Digit 19 = 0

Also seen as

Prime neighborhood

Adjacent primes:

Previous prime: 17 (gap of 2)
Next prime: 23 (gap of 4)

Pair status: twin with 17, cousin with 23.

ASCII character

As an ASCII codepoint, 19 is control character (0x13). ASCII control character.

Hex color

#000013

RGB(0, 0, 19)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.19.

Address: 0.0.0.19
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.0.19

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

US numbered highway

Matches numbered highway designation:

I-19 — Tucson, AZ to Nogales, AZ (Mexico border).

Interstate 19 on Wikipedia ↗

Musical pitch

Heard as a frequency, 19 Hz is closest to:

Concert pitch (A4 = 440 Hz): D♯0 (-40¢)
Scientific pitch (C4 = 256 Hz): D♯0 (-2¢)

Atomic number

On the periodic table, atomic number 19 is Potassium (K) — period 4.

Potassium on Wikipedia ↗