84
84 is a composite number, even, a calendar year.
84 (eighty-four) is an even 2-digit number. It is a composite number with 12 divisors, and factors as 2² × 3 × 7. Its proper divisors sum to 140, more than the number itself, making it an abundant number. Written other ways, in Roman numerals it is LXXXIV and in binary, 1010100.
Interestingness
Historical context — 84 AD
Calendar year
AD 84 (LXXXIV) was a leap year starting on Thursday of the Julian calendar.
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Historical context — 84 BC
Calendar year
Year 84 BC was a year of the pre-Julian Roman calendar.
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Year facts
- Year type
-
Leap year
Divisible by 4 and not by 100; February has 29 days.
- Days in year
- 366
- ISO weeks
- 52
- Started on
-
Saturday
January 1, 84
- Ended on
-
Sunday
December 31, 84
- Friday the 13ths
-
1
One Friday the 13th this year.
- Decade
-
80s
80–89
- Century
-
1st century
1–100
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,942
1942 years before 2026.
In other calendars
- Hebrew
-
3844 / 3845 AM
Rosh Hashanah falls in September/October.
- Chinese
-
Year of the zodiac:Wood zodiac:Monkey
Sexagenary cycle position 21 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
627 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
76 / 77 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
6 / 5 Saka
Indian national calendar; year starts in March.
Properties
Primality
Prime factorization: 2 2 × 3 × 7
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√84 = [9; (6, 18)]
Period length 2 — the block in parentheses repeats forever.
Representations
- In words
- eighty-four
- Ordinal
- 84th
- Roman numeral
- LXXXIV
- Binary
- 1010100
- Octal
- 124
- Hexadecimal
- 0x54
- Base64
- VA==
- One's complement
- 171 (8-bit)
- Scientific notation
- 8.4 × 10¹
- As a duration
- 84 s = 1 minute, 24 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒁹 𒌋𒌋𒁹𒁹𒁹𒁹
- Egyptian hieroglyphic
- 𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓏺𓏺𓏺𓏺
- Greek (Milesian)
- πδʹ
- Mayan (base 20)
- 𝋤·𝋤
- Chinese
- 八十四
- Chinese (financial)
- 捌拾肆
Digit at this position in famous constants
- π — Pi (π)
- Digit 84 = 2
- e — Euler's number (e)
- Digit 84 = 7
- φ — Golden ratio (φ)
- Digit 84 = 0
- √2 — Pythagoras's (√2)
- Digit 84 = 5
- ln 2 — Natural log of 2
- Digit 84 = 0
- γ — Euler-Mascheroni (γ)
- Digit 84 = 3
Also seen as
Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 84, here are decompositions:
- 5 + 79 = 84
- 11 + 73 = 84
- 13 + 71 = 84
- 17 + 67 = 84
- 23 + 61 = 84
- 31 + 53 = 84
- 37 + 47 = 84
- 41 + 43 = 84
Showing the first eight; more decompositions exist.
As an ASCII codepoint, 84 is T. Printable ASCII character T.
As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.84.
- Address
- 0.0.0.84
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.0.84
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Matches numbered highway designation:
- I-84 — Two segments: Portland, OR→Echo, UT and Scranton, PA→Sturbridge, MA.
Heard as a frequency, 84 Hz is closest to:
- Concert pitch (A4 = 440 Hz): E2 (82.4 Hz, +33¢)
- Scientific pitch (C4 = 256 Hz): F2 (85.4 Hz, -29¢)
- Baroque pitch (A4 = 415 Hz): F2 (82.3 Hz, +34¢)
As a MIDI note number, 84 is C6 (1046.5 Hz at concert pitch).
On the periodic table, atomic number 84 is Polonium (Po) — period 6.
Related reading
- Babylonian numerals — The base-60 cuneiform system that gave us 60 minutes, 60 seconds, and 360°.