Number

191

191 is a prime, odd, a calendar year.

Arithmetic Number Chen Prime Deficient Number Flippable Odious Number Palindrome Pernicious Number Prime Recamán's Sequence Sexy Prime Sophie Germain Prime Squarefree Twin Prime Year

Historical context — 191 AD

Calendar year

Year 191 (CXCI) was a common year starting on Friday of the Julian calendar.

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Historical context — 191 BC

Calendar year

Year 191 BC was a year of the pre-Julian Roman 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: Saturday
January 1, 191
Ended on: Saturday
December 31, 191
Friday the 13ths: 1
One Friday the 13th this year.
Decade: 190s
190–199
Century: 2nd century
101–200
Millennium: 1st millennium
1–1000
Years ago: 1,835
1835 years before 2026.

In other calendars

Hebrew: 3951 / 3952 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Metal zodiac:Goat
Sexagenary cycle position 8 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 734 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: 183 / 184 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 113 / 112 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 3
Digit sum: 11
Digit product: 9
Digital root: 2
Palindrome: Yes
Bit width: 8 bits
Flips to (rotate 180°): 161
Recamán's sequence: a(1,389) = 191
Square (n²): 36,481
Cube (n³): 6,967,871
Divisor count: 2
σ(n) — sum of divisors: 192
φ(n) — Euler's totient: 190

Primality

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

Divisors & multiples

All divisors (2)

1 · 191

Aliquot sum (sum of proper divisors): 1

Factor pairs (a × b = 191)

1 × 191

First multiples

191 · 382 (double) · 573 · 764 · 955 · 1,146 · 1,337 · 1,528 · 1,719 · 1,910

Sums & aliquot sequence

As consecutive integers: 95 + 96

Representations

In words: one hundred ninety-one
Ordinal: 191st
Roman numeral: CXCI
Binary: 10111111
Octal: 277
Hexadecimal: 0xBF
Base64: vw==
One's complement: 64 (8-bit)

In other bases

ternary (3) 21002

quaternary (4) 2333

quinary (5) 1231

senary (6) 515

septenary (7) 362

nonary (9) 232

undecimal (11) 164

duodecimal (12) 13b

tridecimal (13) 119

tetradecimal (14) d9

pentadecimal (15) cb

Historical numeral systems

Babylonian (base 60): 𒁹𒁹𒁹 𒌋𒁹
Egyptian hieroglyphic: 𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓏺
Greek (Milesian): ρϟαʹ
Mayan (base 20): 𝋩·𝋫
Chinese: 一百九十一
Chinese (financial): 壹佰玖拾壹

In other modern scripts

Eastern Arabic ١٩١ Devanagari १९१ Bengali ১৯১ Tamil ௧௯௧ Thai ๑๙๑ Tibetan ༡༩༡ Khmer ១៩១ Lao ໑໙໑ Burmese ၁၉၁

Digit at this position in famous constants

π — Pi (π): Digit 191 = 9
e — Euler's number (e): Digit 191 = 1
φ — Golden ratio (φ): Digit 191 = 9
√2 — Pythagoras's (√2): Digit 191 = 7
ln 2 — Natural log of 2: Digit 191 = 6
γ — Euler-Mascheroni (γ): Digit 191 = 2

Also seen as

Prime neighborhood

Adjacent primes:

Previous prime: 181 (gap of 10)
Next prime: 193 (gap of 2)

Pair status: twin with 193.

Unicode codepoint

Inverted Question Mark

U+00BF

Other punctuation (Po)

UTF-8 encoding: C2 BF (2 bytes).

Lookup U+00BF on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#0000BF

RGB(0, 0, 191)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.191.

Address: 0.0.0.191
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.0.191

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