Number

401

401 is a prime, odd, a calendar year.

Arithmetic Number Chen Prime Cousin Prime Deficient Number Evil Number Prime Pythagorean Prime Recamán's Sequence Squarefree Year

Historical context — 401 AD

Calendar year

Year 401 (CDI) was a common year starting on Tuesday of the Julian calendar.

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Historical context — 401 BC

Calendar year

Year 401 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: Monday
January 1, 401
Ended on: Monday
December 31, 401
Friday the 13ths: 2
2 Friday the 13ths this year.
Decade: 400s
400–409
Century: 5th century
401–500
Millennium: 1st millennium
1–1000
Years ago: 1,625
1625 years before 2026.

In other calendars

Hebrew: 4161 / 4162 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Metal zodiac:Ox
Sexagenary cycle position 38 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 944 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: 393 / 394 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 323 / 322 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 3
Digit sum: 5
Digit product: 0
Digital root: 5
Palindrome: No
Bit width: 9 bits
Reversed: 104
Recamán's sequence: a(2,450) = 401
Square (n²): 160,801
Cube (n³): 64,481,201
Divisor count: 2
σ(n) — sum of divisors: 402
φ(n) — Euler's totient: 400

Primality

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

Divisors & multiples

All divisors (2)

1 · 401

Aliquot sum (sum of proper divisors): 1

Factor pairs (a × b = 401)

1 × 401

First multiples

401 · 802 (double) · 1,203 · 1,604 · 2,005 · 2,406 · 2,807 · 3,208 · 3,609 · 4,010

Sums & aliquot sequence

As a sum of two squares: 1² + 20²

As consecutive integers: 200 + 201

Representations

In words: four hundred one
Ordinal: 401st
Roman numeral: CDI
Binary: 110010001
Octal: 621
Hexadecimal: 0x191
Base64: AZE=
One's complement: 65,134 (16-bit)

In other bases

ternary (3) 112212

quaternary (4) 12101

quinary (5) 3101

senary (6) 1505

septenary (7) 1112

nonary (9) 485

undecimal (11) 335

duodecimal (12) 295

tridecimal (13) 24b

tetradecimal (14) 209

pentadecimal (15) 1bb

Historical numeral systems

Babylonian (base 60): 𒁹𒁹𒁹𒁹𒁹𒁹 𒌋𒌋𒌋𒌋𒁹
Egyptian hieroglyphic: 𓍢𓍢𓍢𓍢𓏺
Greek (Milesian): υαʹ
Mayan (base 20): 𝋡·𝋠·𝋡
Chinese: 四百零一
Chinese (financial): 肆佰零壹

In other modern scripts

Eastern Arabic ٤٠١ Devanagari ४०१ Bengali ৪০১ Tamil ௪௦௧ Thai ๔๐๑ Tibetan ༤༠༡ Khmer ៤០១ Lao ໔໐໑ Burmese ၄၀၁

Digit at this position in famous constants

π — Pi (π): Digit 401 = 4
e — Euler's number (e): Digit 401 = 6
φ — Golden ratio (φ): Digit 401 = 8
√2 — Pythagoras's (√2): Digit 401 = 1
ln 2 — Natural log of 2: Digit 401 = 2
γ — Euler-Mascheroni (γ): Digit 401 = 2

Also seen as

Prime neighborhood

Adjacent primes:

Previous prime: 397 (gap of 4)
Next prime: 409 (gap of 8)

Pair status: cousin with 397.

Unicode codepoint

Latin Capital Letter F With Hook

U+0191

Uppercase letter (Lu)

UTF-8 encoding: C6 91 (2 bytes).

Lookup U+0191 on Compart ↗ Lookup on FileFormat.Info ↗

HTTP status code

HTTP 401 Unauthorized — Authentication is required and has failed or not been provided.

4xx class: Client Error.

Hex color

#000191

RGB(0, 1, 145)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.1.145.

Address: 0.0.1.145
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.1.145

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

NANP area code 401

The number 401 is an active NANP area code (North American Numbering Plan).

Primary area: Statewide
Region: Rhode Island
Country: United States

Most NANP area codes have multiple overlays in dense regions; the primary area listed is the historic/largest population center for this code.

Look up area code 401 ↗