55
55 is a composite number, odd, a calendar year.
55 (fifty-five) is an odd 2-digit number. It is a composite number with 4 divisors, and factors as 5 × 11. It is the tenth triangular number and a Fibonacci number. Its digits read the same forwards and backwards, so it is a palindromic number. Written other ways, in Roman numerals it is LV and in binary, 110111.
Interestingness
Historical context — 55 AD
Calendar year
AD 55 (LV) was a common year starting on Wednesday of the Julian calendar.
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Notable events — 55 BC
- Aug 26 Julius Caesar makes his first expedition to Britain.
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
-
Friday
January 1, 55
- Ended on
-
Friday
December 31, 55
- Friday the 13ths
-
1
One Friday the 13th this year.
- Decade
-
50s
50–59
- Century
-
1st century
1–100
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,971
1971 years before 2026.
In other calendars
- Hebrew
-
3815 / 3816 AM
Rosh Hashanah falls in September/October.
- Chinese
-
Year of the zodiac:Wood zodiac:Rabbit
Sexagenary cycle position 52 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
598 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
47 / 48 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
-23 / -24 Saka
Indian national calendar; year starts in March.
Properties
Primality
Prime factorization: 5 × 11
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√55 = [7; (2, 2, 2, 14)]
Period length 4 — the block in parentheses repeats forever.
Representations
- In words
- fifty-five
- Ordinal
- 55th
- Roman numeral
- LV
- Binary
- 110111
- Octal
- 67
- Hexadecimal
- 0x37
- Base64
- Nw==
- One's complement
- 200 (8-bit)
- Scientific notation
- 5.5 × 10¹
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒌋𒌋𒌋𒌋𒌋𒁹𒁹𒁹𒁹𒁹
- Egyptian hieroglyphic
- 𓎆𓎆𓎆𓎆𓎆𓏺𓏺𓏺𓏺𓏺
- Greek (Milesian)
- νεʹ
- Mayan (base 20)
- 𝋢·𝋯
- Chinese
- 五十五
- Chinese (financial)
- 伍拾伍
Digit at this position in famous constants
- π — Pi (π)
- Digit 55 = 0
- e — Euler's number (e)
- Digit 55 = 4
- φ — Golden ratio (φ)
- Digit 55 = 2
- √2 — Pythagoras's (√2)
- Digit 55 = 3
- ln 2 — Natural log of 2
- Digit 55 = 4
- γ — Euler-Mascheroni (γ)
- Digit 55 = 8
Also seen as
As an ASCII codepoint, 55 is 7. Printable ASCII character 7.
As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.55.
- Address
- 0.0.0.55
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.0.55
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Matches numbered highway designation:
- I-55 — LaPlace, LA to Chicago, IL.
Heard as a frequency, 55 Hz is closest to:
- Concert pitch (A4 = 440 Hz): A1 (55 Hz, exact)
- Scientific pitch (C4 = 256 Hz): A1 (53.8 Hz, +38¢)
- Baroque pitch (A4 = 415 Hz): A♯1 (55 Hz, +1¢)
As a MIDI note number, 55 is G3 (196 Hz at concert pitch).
On the periodic table, atomic number 55 is Caesium (Cs) — period 6.
Related reading
- Fibonacci numbers — The sequence where each term is the sum of the two before it — and why it turns up everywhere.
- Triangular numbers — 1, 3, 6, 10, 15 … the counting numbers stacked into triangles, and Gauss's famous shortcut for summing them.
- Egyptian hieroglyphic numerals — Seven hieroglyphs for every power of ten, from a single stroke to a million.