Number

1

1 — One

1 is odd, a calendar year.

One is the multiplicative identity. It is the only positive integer that is neither prime nor composite, and is the first and second number in the Fibonacci sequence.

Sources https://en.wikipedia.org/wiki/1

Arithmetic Number Automorphic Number Bell Number Catalan Number Curated Deficient Number Dudeney Number Factorial Factorion Fibonacci Flippable Happy Number Harshad / Niven Heptagonal Hexagonal Highly Abundant Highly Composite Number Jacobsthal Number Kaprekar Number Lucas Markov Number Motzkin Number Münchhausen Number Narcissistic / Armstrong Octagonal Odious Number Padovan Number Partition Number Pell Number Pentagonal Perfect Cube Perfect Square Power of Ten Power of Two Practical Number Recamán's Sequence Refactorable Number Repunit Self Number Strobogrammatic Tetranacci Number Triangular Tribonacci Number Woodall Number Zuckerman Number

Interestingness

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42 notable facts · grade A

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Historical context — 1 AD

First 9 years of the Common Era

The 0s began on January 1, AD 1 and ended on December 31, AD 9, covering the first nine years of the Common Era.

Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 Read the full article on Wikipedia →

Historical context — 1 BC

Calendar year

Year 1 BC was a common year starting on Friday or Saturday in the Julian calendar and a leap year starting on Thursday in the proleptic Julian calendar.

Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 Read the full article on Wikipedia →

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: Monday
January 1, 1
Ended on: Monday
December 31, 1
Friday the 13ths: 2
2 Friday the 13ths this year.
Decade: 0s
0–9
Century: 1st century
1–100
Millennium: 1st millennium
1–1000
Years ago: 2,025
2025 years before 2026.

In other calendars

Hebrew: 3761 / 3762 AM
Rosh Hashanah falls in September/October.
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: 544 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: -7 / -6 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): -77 / -78 Saka
Indian national calendar; year starts in March.

Properties

Parity: Odd
Digit count: 1
Digit sum: 1
Digital root: 1
Palindrome: Yes
Bit width: 1 bits
Recamán's sequence: a(1) = 1
Square (n²): 1
Cube (n³): 1
Square root (√n): 1
Cube root (∛n): 1
Divisor count: 1
σ(n) — sum of divisors: 1
φ(n) — Euler's totient: 1

Divisors & multiples

All divisors (1)

Aliquot sum (sum of proper divisors): 0

Factor pairs (a × b = 1)

1 × 1

First multiples

1 · 2 (double) · 3 · 4 · 5 · 6 · 7 · 8 · 9 · 10

Sums & aliquot sequence

As a sum of two squares: 0² + 1²

Representations

In words: one
Ordinal: 1st
Roman numeral: I
Binary: 1
Octal: 1
Hexadecimal: 0x1
Base64: AQ==
One's complement: 254 (8-bit)

In other bases

ternary (3) 1

quaternary (4) 1

quinary (5) 1

senary (6) 1

septenary (7) 1

nonary (9) 1

undecimal (11) 1

duodecimal (12) 1

tridecimal (13) 1

tetradecimal (14) 1

pentadecimal (15) 1

As an angle

1°

1° ≈ 0.017 rad

Compass bearing: N (north)

Why does a circle have 360 degrees? →

Historical numeral systems

Babylonian (base 60): 𒁹
Egyptian hieroglyphic: 𓏺
Greek (Milesian): αʹ
Mayan (base 20): 𝋡
Chinese: 一
Chinese (financial): 壹

In other modern scripts

Eastern Arabic ١ Devanagari १ Bengali ১ Tamil ௧ Thai ๑ Tibetan ༡ Khmer ១ Lao ໑ Burmese ၁

Digit at this position in famous constants

π — Pi (π): Digit 1 = 3
e — Euler's number (e): Digit 1 = 2
φ — Golden ratio (φ): Digit 1 = 1
√2 — Pythagoras's (√2): Digit 1 = 1
ln 2 — Natural log of 2: Digit 1 = 0
γ — Euler-Mascheroni (γ): Digit 1 = 0

Also seen as

ASCII character

As an ASCII codepoint, 1 is control character (0x01). ASCII control character.

Hex color

#000001

RGB(0, 0, 1)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.1.

Address: 0.0.0.1
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.0.1

Unspecified address (0.0.0.0/8) — "this network" placeholder.

US numbered highway

Matches numbered highway designation:

US 1 — Fort Kent, ME to Key West, FL — the east-coast US Route, predates the Interstate system.

US 1 on Wikipedia ↗

Musical pitch

As a MIDI note number, 1 is C♯-1 (8.7 Hz at concert pitch). (below the ~20 Hz floor of human hearing — likely inaudible)

Atomic number

On the periodic table, atomic number 1 is Hydrogen (H) — period 1.

Hydrogen on Wikipedia ↗