Number

661

661 is a prime, odd, a calendar year.

Arithmetic Number Deficient Number Flippable Odious Number Pernicious Number Prime Pythagorean Prime Recamán's Sequence Squarefree Twin Prime Year

Historical context — 661 AD

Calendar year

Year 661 (DCLXI) was a common year starting on Friday of the Julian calendar.

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Historical context — 661 BC

Calendar year

The year 661 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: Tuesday
January 1, 661
Ended on: Tuesday
December 31, 661
Friday the 13ths: 2
2 Friday the 13ths this year.
Decade: 660s
660–669
Century: 7th century
601–700
Millennium: 1st millennium
1–1000
Years ago: 1,365
1365 years before 2026.

In other calendars

Hebrew: 4421 / 4422 AM
Rosh Hashanah falls in September/October.
Islamic Hijri: 40 / 41 AH
Lunar calendar; year spans differ from Gregorian.
Chinese: Year of the zodiac:Metal zodiac:Rooster
Sexagenary cycle position 58 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 1204 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Persian Solar Hijri: 39 / 40 SH
Iranian calendar; Nowruz (new year) falls on the spring equinox.
Ethiopian: 653 / 654 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 583 / 582 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 3
Digit sum: 13
Digit product: 36
Digital root: 4
Palindrome: No
Bit width: 10 bits
Reversed: 166
Flips to (rotate 180°): 199
Recamán's sequence: a(2,302) = 661
Square (n²): 436,921
Cube (n³): 288,804,781
Divisor count: 2
σ(n) — sum of divisors: 662
φ(n) — Euler's totient: 660

Primality

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

Divisors & multiples

All divisors (2)

1 · 661

Aliquot sum (sum of proper divisors): 1

Factor pairs (a × b = 661)

1 × 661

First multiples

661 · 1,322 (double) · 1,983 · 2,644 · 3,305 · 3,966 · 4,627 · 5,288 · 5,949 · 6,610

Sums & aliquot sequence

As a sum of two squares: 6² + 25²

As consecutive integers: 330 + 331

Representations

In words: six hundred sixty-one
Ordinal: 661st
Roman numeral: DCLXI
Binary: 1010010101
Octal: 1225
Hexadecimal: 0x295
Base64: ApU=
One's complement: 64,874 (16-bit)

In other bases

ternary (3) 220111

quaternary (4) 22111

quinary (5) 10121

senary (6) 3021

septenary (7) 1633

nonary (9) 814

undecimal (11) 551

duodecimal (12) 471

tridecimal (13) 3bb

tetradecimal (14) 353

pentadecimal (15) 2e1

Historical numeral systems

Babylonian (base 60): 𒌋𒁹 𒁹
Egyptian hieroglyphic: 𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓏺
Greek (Milesian): χξαʹ
Mayan (base 20): 𝋡·𝋭·𝋡
Chinese: 六百六十一
Chinese (financial): 陸佰陸拾壹

In other modern scripts

Eastern Arabic ٦٦١ Devanagari ६६१ Bengali ৬৬১ Tamil ௬௬௧ Thai ๖๖๑ Tibetan ༦༦༡ Khmer ៦៦១ Lao ໖໖໑ Burmese ၆၆၁

Digit at this position in famous constants

π — Pi (π): Digit 661 = 1
e — Euler's number (e): Digit 661 = 8
φ — Golden ratio (φ): Digit 661 = 3
√2 — Pythagoras's (√2): Digit 661 = 8
ln 2 — Natural log of 2: Digit 661 = 2
γ — Euler-Mascheroni (γ): Digit 661 = 0

Also seen as

Prime neighborhood

Adjacent primes:

Previous prime: 659 (gap of 2)
Next prime: 673 (gap of 12)

Pair status: twin with 659.

Unicode codepoint

Latin Letter Pharyngeal Voiced Fricative

U+0295

Lowercase letter (Ll)

UTF-8 encoding: CA 95 (2 bytes).

Lookup U+0295 on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#000295

RGB(0, 2, 149)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.2.149.

Address: 0.0.2.149
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.2.149

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

NANP area code 661

The number 661 is an active NANP area code (North American Numbering Plan).

Primary area: Bakersfield / Santa Clarita
Region: California
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 661 ↗