1,581
1,581 is a composite number, odd, a calendar year.
1,581 (one thousand five hundred eighty-one) is an odd 4-digit number. It is a composite number with 8 divisors, and factors as 3 × 17 × 31. Written other ways, in Roman numerals it is MDLXXXI and in binary, 11000101101.
Interestingness
Notable events — 1581 AD
- Jul 26 The Dutch issue the Act of Abjuration, deposing Philip II.
- Sep 8 Tsar Ivan IV kills his son Ivan in a rage.
- Aug 26 Russian Cossack Yermak begins the conquest of Siberia.
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
-
53
Long year: contains 53 ISO weeks.
- Started on
-
Thursday
January 1, 1581
- Ended on
-
Thursday
December 31, 1581
- Friday the 13ths
-
3
3 Friday the 13ths this year.
- Decade
-
1580s
1580–1589
- Century
-
16th century
1501–1600
- Millennium
-
2nd millennium
1001–2000
- Years ago
-
445
445 years before 2026.
In other calendars
- Hebrew
-
5341 / 5342 AM
Rosh Hashanah falls in September/October.
- Islamic Hijri
-
988 / 989 AH
Lunar calendar; year spans differ from Gregorian.
- 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
-
2124 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Persian Solar Hijri
-
959 / 960 SH
Iranian calendar; Nowruz (new year) falls on the spring equinox.
- Ethiopian
-
1573 / 1574 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
1503 / 1502 Saka
Indian national calendar; year starts in March.
Properties
Primality
Prime factorization: 3 × 17 × 31
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√1,581 = [39; (1, 3, 5, 19, 1, 2, 4, 2, 1, 19, 5, 3, 1, 78)]
Period length 14 — the block in parentheses repeats forever.
Representations
- In words
- one thousand five hundred eighty-one
- Ordinal
- 1581st
- Roman numeral
- MDLXXXI
- Binary
- 11000101101
- Octal
- 3055
- Hexadecimal
- 0x62D
- Base64
- Bi0=
- One's complement
- 63,954 (16-bit)
- Scientific notation
- 1.581 × 10³
- As a duration
- 1,581 s = 26 minutes, 21 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒌋𒌋𒁹𒁹𒁹𒁹𒁹𒁹 𒌋𒌋𒁹
- Egyptian hieroglyphic
- 𓆼𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓏺
- Greek (Milesian)
- ͵αφπαʹ
- Mayan (base 20)
- 𝋣·𝋳·𝋡
- Chinese
- 一千五百八十一
- Chinese (financial)
- 壹仟伍佰捌拾壹
Digit at this position in famous constants
- π — Pi (π)
- Digit 1,581 = 7
- e — Euler's number (e)
- Digit 1,581 = 0
- φ — Golden ratio (φ)
- Digit 1,581 = 5
- √2 — Pythagoras's (√2)
- Digit 1,581 = 1
- ln 2 — Natural log of 2
- Digit 1,581 = 0
- γ — Euler-Mascheroni (γ)
- Digit 1,581 = 1
Also seen as
UTF-8 encoding: D8 AD (2 bytes).
As an unsigned 32-bit integer, this is the IPv4 address 0.0.6.45.
- Address
- 0.0.6.45
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.6.45
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Heard as a frequency, 1,581 Hz is closest to:
- Concert pitch (A4 = 440 Hz): G6 (1568 Hz, +14¢)
- Scientific pitch (C4 = 256 Hz): G♯6 (1625.5 Hz, -48¢ — about midway to G6)
- Baroque pitch (A4 = 415 Hz): G♯6 (1566.8 Hz, +16¢)
The digit sequence 1581 first appears in π at position 4,362 of the decimal expansion (the 4,362ordinal-suffix:nd 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
- Babylonian numerals — The base-60 cuneiform system that gave us 60 minutes, 60 seconds, and 360°.