1,861
1,861 is a prime, odd, a calendar year.
1,861 (one thousand eight hundred sixty-one) is an odd 4-digit number. It is a prime number — divisible only by 1 and itself. Written other ways, in Roman numerals it is MDCCCLXI and in binary, 11101000101.
Interestingness
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
Primality
1,861 is prime. It has exactly two divisors: 1 and itself.
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√1,861 = [43; (7, 5, 1, 1, 1, 1, 3, 1, 2, 2, 2, 2, 1, 3, 1, 1, 1, 1, 5, 7, 86)]
Period length 21 — the block in parentheses repeats forever.
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)
- Scientific notation
- 1.861 × 10³
- As a duration
- 1,861 s = 31 minutes, 1 second
As an angle
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
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
UTF-8 encoding: DD 85 (2 bytes).
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.
Heard as a frequency, 1,861 Hz is closest to:
- Concert pitch (A4 = 440 Hz): A♯6 (1864.7 Hz, -3¢)
- Scientific pitch (C4 = 256 Hz): A♯6 (1824.6 Hz, +34¢)
- Baroque pitch (A4 = 415 Hz): B6 (1863.3 Hz, -2¢)
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.
Related reading
- Prime numbers — The building blocks of arithmetic: what primes are, why they matter, and how we find them.
- Egyptian hieroglyphic numerals — Seven hieroglyphs for every power of ten, from a single stroke to a million.