Number

2

2 — The Only Even Prime

2 is a prime, even, a calendar year.

Two is the smallest and only even prime number. Every other prime is odd, since any larger even number is divisible by 2.

Sources https://en.wikipedia.org/wiki/2

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Interestingness

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Historical context — 2 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 — 2 BC

Calendar year

Year 2 BC was a common year starting on Thursday or Friday of the Julian calendar and a common year starting on Wednesday of 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: Tuesday
January 1, 2
Ended on: Tuesday
December 31, 2
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: 2,024
2024 years before 2026.

In other calendars

Hebrew: 3762 / 3763 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Water zodiac:Dog
Sexagenary cycle position 59 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 545 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: -6 / -5 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): -76 / -77 Saka
Indian national calendar; year starts in March.

Properties

Parity: Even
Digit count: 1
Digit sum: 2
Digital root: 2
Palindrome: Yes
Bit width: 2 bits
Recamán's sequence: a(4) = 2
Square (n²): 4
Cube (n³): 8
Divisor count: 2
σ(n) — sum of divisors: 3
φ(n) — Euler's totient: 1

Primality

2 is prime. It has exactly two divisors: 1 and itself.

Divisors & multiples

All divisors (2)

1 (half) · 2

Aliquot sum (sum of proper divisors): 1

Factor pairs (a × b = 2)

1 × 2

First multiples

2 · 4 (double) · 6 · 8 · 10 · 12 · 14 · 16 · 18 · 20

Sums & aliquot sequence

As a sum of two squares: 1² + 1²

As a sum of two cubes: 1³ + 1³

Continued fraction of √n

√2 = [1; (2)]

Period length 1 — the block in parentheses repeats forever.

Representations

In words: two
Ordinal: 2nd
Roman numeral: II
Binary: 10
Octal: 2
Hexadecimal: 0x2
Base64: Ag==
One's complement: 253 (8-bit)

In other bases

ternary (3) 2

quaternary (4) 2

quinary (5) 2

senary (6) 2

septenary (7) 2

nonary (9) 2

undecimal (11) 2

duodecimal (12) 2

tridecimal (13) 2

tetradecimal (14) 2

pentadecimal (15) 2

As an angle

2°

2° ≈ 0.035 rad

Compass bearing: N (north)

Why does a circle have 360 degrees? →

Historical numeral systems

Babylonian (base 60): 𒁹𒁹
Egyptian hieroglyphic: 𓏺𓏺
Greek (Milesian): βʹ
Mayan (base 20): 𝋢
Chinese: 二
Chinese (financial): 貳

In other modern scripts

Eastern Arabic ٢ Devanagari २ Bengali ২ Tamil ௨ Thai ๒ Tibetan ༢ Khmer ២ Lao ໒ Burmese ၂

Digit at this position in famous constants

π — Pi (π): Digit 2 = 1
e — Euler's number (e): Digit 2 = 7
φ — Golden ratio (φ): Digit 2 = 6
√2 — Pythagoras's (√2): Digit 2 = 4
ln 2 — Natural log of 2: Digit 2 = 6
γ — Euler-Mascheroni (γ): Digit 2 = 5

Also seen as

Prime neighborhood

Adjacent primes:

Next prime: 3 (gap of 1)

ASCII character

As an ASCII codepoint, 2 is control character (0x02). ASCII control character.

Hex color

#000002

RGB(0, 0, 2)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.2.

Address: 0.0.0.2
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.0.2

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

Musical pitch

As a MIDI note number, 2 is D-1 (9.2 Hz at concert pitch). (below the ~20 Hz floor of human hearing — likely inaudible)

Atomic number

On the periodic table, atomic number 2 is Helium (He) — period 1.

Helium on Wikipedia ↗