101
101 is a prime, odd, a calendar year.
101 (one hundred one) is an odd 3-digit number. It is a prime number — divisible only by 1 and itself. Its digits read the same forwards and backwards, so it is a palindromic number. Written other ways, in Roman numerals it is CI and in binary, 1100101.
Interestingness
Historical context — 101 AD
Calendar year
Year 101 (CI) was a common year starting on Friday of the Julian calendar.
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Historical context — 101 BC
Calendar year
Year 101 BC was a year of the pre-Julian Roman calendar.
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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
-
Saturday
January 1, 101
- Ended on
-
Saturday
December 31, 101
- Friday the 13ths
-
1
One Friday the 13th this year.
- Decade
-
100s
100–109
- Century
-
2nd century
101–200
- Millennium
-
1st millennium
1–1000
- Years ago
-
1,925
1925 years before 2026.
In other calendars
- Hebrew
-
3861 / 3862 AM
Rosh Hashanah falls in September/October.
- Chinese
-
Year of the zodiac:Metal zodiac:Ox
Sexagenary cycle position 38 of 60. Lunar new year falls in late January / mid-February.
- Buddhist Era
-
644 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
- Ethiopian
-
93 / 94 ET
Year boundary at Enkutatash (September 11/12).
- Indian National (Saka)
-
23 / 22 Saka
Indian national calendar; year starts in March.
Properties
Primality
101 is prime. It has exactly two divisors: 1 and itself.
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√101 = [10; (20)]
Period length 1 — the block in parentheses repeats forever.
Representations
- In words
- one hundred one
- Ordinal
- 101st
- Roman numeral
- CI
- Binary
- 1100101
- Octal
- 145
- Hexadecimal
- 0x65
- Base64
- ZQ==
- One's complement
- 154 (8-bit)
- Scientific notation
- 1.01 × 10²
- As a duration
- 101 s = 1 minute, 41 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒁹 𒌋𒌋𒌋𒌋𒁹
- Egyptian hieroglyphic
- 𓍢𓏺
- Greek (Milesian)
- ραʹ
- Mayan (base 20)
- 𝋥·𝋡
- Chinese
- 一百零一
- Chinese (financial)
- 壹佰零壹
Digit at this position in famous constants
- π — Pi (π)
- Digit 101 = 9
- e — Euler's number (e)
- Digit 101 = 4
- φ — Golden ratio (φ)
- Digit 101 = 4
- √2 — Pythagoras's (√2)
- Digit 101 = 7
- ln 2 — Natural log of 2
- Digit 101 = 5
- γ — Euler-Mascheroni (γ)
- Digit 101 = 5
Also seen as
As an ASCII codepoint, 101 is e. Printable ASCII character e.
HTTP 101 Switching Protocols — Server is switching protocols at the client's request (e.g., to WebSocket).
1xx class: Informational.
As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.101.
- Address
- 0.0.0.101
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.0.101
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Matches numbered highway designation:
- US 101 — Tumwater, WA to Los Angeles, CA — the Pacific Coast highway.
Heard as a frequency, 101 Hz is closest to:
- Concert pitch (A4 = 440 Hz): G♯2 (103.8 Hz, -48¢ — about midway to G2)
- Scientific pitch (C4 = 256 Hz): G♯2 (101.6 Hz, -10¢)
- Baroque pitch (A4 = 415 Hz): A2 (103.8 Hz, -47¢ — about midway to G♯2)
As a MIDI note number, 101 is F7 (2793.8 Hz at concert pitch).
On the periodic table, atomic number 101 is Mendelevium (Md) — period 7.
On an ingredients label, E101 is Riboflavin, a food colour — vitamin B2.
Related reading
- Prime numbers — The building blocks of arithmetic: what primes are, why they matter, and how we find them.
- Mayan numerals — Vigesimal dots-and-bars with a shell zero — one of the earliest true zeros.