Number

261

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

Arithmetic Number Deficient Number Harshad / Niven Nonagonal Odious Number Pernicious Number Recamán's Sequence Year

Historical context — 261 AD

Calendar year

Year 261 (CCLXI) was a common year starting on Tuesday of the Julian calendar.

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Historical context — 261 BC

Calendar year

Year 261 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, 261
Ended on: Tuesday
December 31, 261
Friday the 13ths: 2
2 Friday the 13ths this year.
Decade: 260s
260–269
Century: 3rd century
201–300
Millennium: 1st millennium
1–1000
Years ago: 1,765
1765 years before 2026.

In other calendars

Hebrew: 4021 / 4022 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Metal zodiac:Snake
Sexagenary cycle position 18 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 804 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: 253 / 254 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 183 / 182 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 3
Digit sum: 9
Digit product: 12
Digital root: 9
Palindrome: No
Bit width: 9 bits
Reversed: 162
Recamán's sequence: a(109) = 261
Square (n²): 68,121
Cube (n³): 17,779,581
Divisor count: 6
σ(n) — sum of divisors: 390
φ(n) — Euler's totient: 168
Sum of prime factors: 35

Primality

Prime factorization: 3 ² × 29

Nearest primes: 257 (−4) · 263 (+2)

Divisors & multiples

All divisors (6)

1 · 3 · 9 · 29 · 87 · 261

Aliquot sum (sum of proper divisors): 129

Factor pairs (a × b = 261)

1 × 261

3 × 87

9 × 29

First multiples

261 · 522 (double) · 783 · 1,044 · 1,305 · 1,566 · 1,827 · 2,088 · 2,349 · 2,610

Sums & aliquot sequence

As a sum of two squares: 6² + 15²

As consecutive integers: 130 + 131 86 + 87 + 88 41 + 42 + 43 + 44 + 45 + 46 25 + 26 + … + 33

Aliquot sequence: 261 → 129 → 47 → 1 → 0 — terminates at zero

Representations

In words: two hundred sixty-one
Ordinal: 261st
Roman numeral: CCLXI
Binary: 100000101
Octal: 405
Hexadecimal: 0x105
Base64: AQU=
One's complement: 65,274 (16-bit)

In other bases

ternary (3) 100200

quaternary (4) 10011

quinary (5) 2021

senary (6) 1113

septenary (7) 522

nonary (9) 320

undecimal (11) 218

duodecimal (12) 199

tridecimal (13) 171

tetradecimal (14) 149

pentadecimal (15) 126

Historical numeral systems

Babylonian (base 60): 𒁹𒁹𒁹𒁹 𒌋𒌋𒁹
Egyptian hieroglyphic: 𓍢𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓏺
Greek (Milesian): σξαʹ
Mayan (base 20): 𝋭·𝋡
Chinese: 二百六十一
Chinese (financial): 貳佰陸拾壹

In other modern scripts

Eastern Arabic ٢٦١ Devanagari २६१ Bengali ২৬১ Tamil ௨௬௧ Thai ๒๖๑ Tibetan ༢༦༡ Khmer ២៦១ Lao ໒໖໑ Burmese ၂၆၁

Digit at this position in famous constants

π — Pi (π): Digit 261 = 2
e — Euler's number (e): Digit 261 = 6
φ — Golden ratio (φ): Digit 261 = 4
√2 — Pythagoras's (√2): Digit 261 = 3
ln 2 — Natural log of 2: Digit 261 = 5
γ — Euler-Mascheroni (γ): Digit 261 = 8

Also seen as

Unicode codepoint

Latin Small Letter A With Ogonek

U+0105

Lowercase letter (Ll)

UTF-8 encoding: C4 85 (2 bytes).

Lookup U+0105 on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#000105

RGB(0, 1, 5)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.1.5.

Address: 0.0.1.5
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.1.5

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