Number

1,861

1,861 is a prime, odd, a calendar year.

Arithmetic Number Deficient Number Evil Number Flippable Prime Pythagorean Prime Recamán's Sequence Sexy Prime Squarefree Year

Notable events — 1861 AD

Mar 4 Abraham Lincoln is inaugurated US president.
Mar 17 The Kingdom of Italy is proclaimed under Victor Emmanuel II.
Apr 12 Confederate forces fire on Fort Sumter, starting the American Civil War.
Jul 21 The First Battle of Bull Run ends in Confederate victory.
Mar 3 Tsar Alexander II issues the Emancipation Reform freeing 23 million Russian serfs.

Events compiled from Wikipedia ↗ · Licensed CC BY-SA 4.0

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, 1861
Ended on: Tuesday
December 31, 1861
Friday the 13ths: 2
2 Friday the 13ths this year.
Easter Sunday: March 31
Sunday, March 31, 1861
Decade: 1860s
1860–1869
Century: 19th century
1801–1900
Millennium: 2nd millennium
1001–2000
Years ago: 165
165 years before 2026.

In other calendars

Hebrew: 5621 / 5622 AM
Rosh Hashanah falls in September/October.
Islamic Hijri: 1277 / 1278 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: 2404 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Persian Solar Hijri: 1239 / 1240 SH
Iranian calendar; Nowruz (new year) falls on the spring equinox.
Ethiopian: 1853 / 1854 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): 1783 / 1782 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 4
Digit sum: 16
Digit product: 48
Digital root: 7
Palindrome: No
Bit width: 11 bits
Reversed: 1,681
Flips to (rotate 180°): 1,981
Recamán's sequence: a(8,022) = 1,861
Square (n²): 3,463,321
Cube (n³): 6,445,240,381
Divisor count: 2
σ(n) — sum of divisors: 1,862
φ(n) — Euler's totient: 1,860

Primality

1,861 is prime. It has exactly two divisors: 1 and itself.

Divisors & multiples

All divisors (2)

1 · 1861

Aliquot sum (sum of proper divisors): 1

Factor pairs (a × b = 1,861)

1 × 1861

First multiples

1,861 · 3,722 (double) · 5,583 · 7,444 · 9,305 · 11,166 · 13,027 · 14,888 · 16,749 · 18,610

Sums & aliquot sequence

As a sum of two squares: 30² + 31²

As consecutive integers: 930 + 931

Representations

In words: one thousand eight hundred sixty-one
Ordinal: 1861st
Roman numeral: MDCCCLXI
Binary: 11101000101
Octal: 3505
Hexadecimal: 0x745
Base64: B0U=
One's complement: 63,674 (16-bit)

In other bases

ternary (3) 2112221

quaternary (4) 131011

quinary (5) 24421

senary (6) 12341

septenary (7) 5266

nonary (9) 2487

undecimal (11) 1442

duodecimal (12) 10b1

tridecimal (13) b02

tetradecimal (14) 96d

pentadecimal (15) 841

Historical numeral systems

Babylonian (base 60): 𒌋𒌋𒌋𒁹 𒁹
Egyptian hieroglyphic: 𓆼𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓏺
Greek (Milesian): ͵αωξαʹ
Mayan (base 20): 𝋤·𝋭·𝋡
Chinese: 一千八百六十一
Chinese (financial): 壹仟捌佰陸拾壹

In other modern scripts

Eastern Arabic ١٨٦١ Devanagari १८६१ Bengali ১৮৬১ Tamil ௧௮௬௧ Thai ๑๘๖๑ Tibetan ༡༨༦༡ Khmer ១៨៦១ Lao ໑໘໖໑ Burmese ၁၈၆၁

Digit at this position in famous constants

π — Pi (π): Digit 1,861 = 6
e — Euler's number (e): Digit 1,861 = 9
φ — Golden ratio (φ): Digit 1,861 = 7
√2 — Pythagoras's (√2): Digit 1,861 = 1
ln 2 — Natural log of 2: Digit 1,861 = 0
γ — Euler-Mascheroni (γ): Digit 1,861 = 6

Also seen as

Prime neighborhood

Adjacent primes:

Previous prime: 1,847 (gap of 14)
Next prime: 1,867 (gap of 6)

Pair status: sexy with 1867.

Unicode codepoint

Syriac Three Dots Above

U+0745

Non-spacing mark (Mn)

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

Lookup U+0745 on Compart ↗ Lookup on FileFormat.Info ↗

Hex color

#000745

RGB(0, 7, 69)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.7.69.

Address: 0.0.7.69
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.7.69

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

Position in π

The digit sequence 1861 first appears in π at position 424 of the decimal expansion (the 424ordinal-suffix:th digit after the integer 3).

Search range: the first 1,000,000 fractional digits of π. Any 6-digit-or-shorter string is virtually guaranteed to appear in there — the more interesting signal is the position.

Look up 1861 on Pi Search ↗