Number

391

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

Arithmetic Number Deficient Number Happy Number Odious Number Pernicious Number Recamán's Sequence Semiprime Smith Number Squarefree Year

Historical context — 391 AD

Calendar year

Year 391 (CCCXCI) was a common year starting on Wednesday of the Julian calendar.

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Historical context — 391 BC

Calendar year

Year 391 BC was a year of the pre-Julian Roman calendar.

Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 · English fallback 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: Tuesday
January 1, 391
Ended on: Tuesday
December 31, 391
Friday the 13ths: 2
2 Friday the 13ths this year.
Decade: 390s
390–399
Century: 4th century
301–400
Millennium: 1st millennium
1–1000
Years ago: 1,635
1635 years before 2026.

In other calendars

Hebrew: 4151 / 4152 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Metal zodiac:Rabbit
Sexagenary cycle position 28 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 934 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: 383 / 384 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 313 / 312 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 3
Digit sum: 13
Digit product: 27
Digital root: 4
Palindrome: No
Bit width: 9 bits
Reversed: 193
Recamán's sequence: a(2,470) = 391
Square (n²): 152,881
Cube (n³): 59,776,471
Divisor count: 4
σ(n) — sum of divisors: 432
φ(n) — Euler's totient: 352
Sum of prime factors: 40

Primality

Prime factorization: 17 × 23

Nearest primes: 389 (−2) · 397 (+6)

Divisors & multiples

All divisors (4)

1 · 17 · 23 · 391

Aliquot sum (sum of proper divisors): 41

Factor pairs (a × b = 391)

1 × 391

17 × 23

First multiples

391 · 782 (double) · 1,173 · 1,564 · 1,955 · 2,346 · 2,737 · 3,128 · 3,519 · 3,910

Sums & aliquot sequence

As consecutive integers: 195 + 196 15 + 16 + … + 31 6 + 7 + … + 28

Aliquot sequence: 391 → 41 → 1 → 0 — terminates at zero

Representations

In words: three hundred ninety-one
Ordinal: 391st
Roman numeral: CCCXCI
Binary: 110000111
Octal: 607
Hexadecimal: 0x187
Base64: AYc=
One's complement: 65,144 (16-bit)

In other bases

ternary (3) 112111

quaternary (4) 12013

quinary (5) 3031

senary (6) 1451

septenary (7) 1066

nonary (9) 474

undecimal (11) 326

duodecimal (12) 287

tridecimal (13) 241

tetradecimal (14) 1dd

pentadecimal (15) 1b1

Historical numeral systems

Babylonian (base 60): 𒁹𒁹𒁹𒁹𒁹𒁹 𒌋𒌋𒌋𒁹
Egyptian hieroglyphic: 𓍢𓍢𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓏺
Greek (Milesian): τϟαʹ
Mayan (base 20): 𝋳·𝋫
Chinese: 三百九十一
Chinese (financial): 參佰玖拾壹

In other modern scripts

Eastern Arabic ٣٩١ Devanagari ३९१ Bengali ৩৯১ Tamil ௩௯௧ Thai ๓๙๑ Tibetan ༣༩༡ Khmer ៣៩១ Lao ໓໙໑ Burmese ၃၉၁

Digit at this position in famous constants

π — Pi (π): Digit 391 = 1
e — Euler's number (e): Digit 391 = 7
φ — Golden ratio (φ): Digit 391 = 7
√2 — Pythagoras's (√2): Digit 391 = 3
ln 2 — Natural log of 2: Digit 391 = 9
γ — Euler-Mascheroni (γ): Digit 391 = 3

Also seen as

Unicode codepoint

Latin Capital Letter C With Hook

U+0187

Uppercase letter (Lu)

UTF-8 encoding: C6 87 (2 bytes).

Lookup U+0187 on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#000187

RGB(0, 1, 135)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.1.135.

Address: 0.0.1.135
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.1.135

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