Number

7

7 — Seven

7 is a prime, odd, a calendar year.

Seven is the fourth prime number and the lowest natural number that cannot be represented as the sum of the squares of three integers. It appears repeatedly across cultures: seven days of the week, seven wonders of the ancient world, seven deadly sins.

Sources https://en.wikipedia.org/wiki/7

Arithmetic Number Chen Prime Cousin Prime Curated Deficient Number Happy Number Harshad / Niven Heptagonal Lucas Lucky Number Mersenne Prime Narcissistic / Armstrong Odious Number Padovan Number Pernicious Number Perrin Number Prime Recamán's Sequence Safe Prime Self Number Sexy Prime Squarefree Tribonacci Number Twin Prime Woodall Number Zuckerman Number

Historical context — 7 AD

Calendar year

AD 7 was a common year starting on Saturday of the Julian calendar.

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

Historical context — 7 BC

Calendar year

Year 7 BC was a common year starting on Saturday or Sunday of the Julian calendar and a common year starting on Thursday of the Proleptic Julian calendar.

Excerpt from Wikipedia (en) ↗ · Licensed CC BY-SA 4.0 · English fallback 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, 7
Ended on: Monday
December 31, 7
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: 2,019
2019 years before 2026.

In other calendars

Hebrew: 3767 / 3768 AM
Rosh Hashanah falls in September/October.
Chinese: Year of the zodiac:Fire zodiac:Rabbit
Sexagenary cycle position 4 of 60. Lunar new year falls in late January / mid-February.
Buddhist Era: 550 BE
Counted from the parinirvana of the Buddha (Theravada / Thai / Sri Lankan convention).
Ethiopian: -1 / 0 ET
Year boundary at Enkutatash (September 11/12).
Indian National (Saka): -71 / -72 Saka
Indian national calendar; year starts in March.

Cultural significance

Western lucky

Widely considered lucky — "lucky number seven."

Seven days of the week, seven seas, seven wonders, seven colors of the rainbow.

Wikipedia ↗

Christian sacred

Represents completeness and perfection.

Seven days of creation, seven sacraments, seven deadly sins, seven heavenly virtues.

Japanese lucky

Associated with the Seven Lucky Gods (Shichifukujin).

Seven gods of fortune in Japanese folklore.

Sourced from Wikipedia (Numerology, Chinese numerology, Gematria, and per-culture articles).

Properties

Parity: Odd
Digit count: 1
Digit sum: 7
Digital root: 7
Palindrome: Yes
Bit width: 3 bits
Recamán's sequence: a(5) = 7
Square (n²): 49
Cube (n³): 343
Divisor count: 2
σ(n) — sum of divisors: 8
φ(n) — Euler's totient: 6

Primality

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

Divisors & multiples

All divisors (2)

1 · 7

Aliquot sum (sum of proper divisors): 1

Factor pairs (a × b = 7)

1 × 7

First multiples

7 · 14 (double) · 21 · 28 · 35 · 42 · 49 · 56 · 63 · 70

Sums & aliquot sequence

As consecutive integers: 3 + 4

Representations

In words: seven
Ordinal: 7th
Roman numeral: VII
Binary: 111
Octal: 7
Hexadecimal: 0x7
Base64: Bw==
One's complement: 248 (8-bit)

In other bases

ternary (3) 21

quaternary (4) 13

quinary (5) 12

senary (6) 11

septenary (7) 10

nonary (9) 7

undecimal (11) 7

duodecimal (12) 7

tridecimal (13) 7

tetradecimal (14) 7

pentadecimal (15) 7

Historical numeral systems

Babylonian (base 60): 𒁹𒁹𒁹𒁹𒁹𒁹𒁹
Egyptian hieroglyphic: 𓏺𓏺𓏺𓏺𓏺𓏺𓏺
Greek (Milesian): ζʹ
Mayan (base 20): 𝋧
Chinese: 七
Chinese (financial): 柒

In other modern scripts

Eastern Arabic ٧ Devanagari ७ Bengali ৭ Tamil ௭ Thai ๗ Tibetan ༧ Khmer ៧ Lao ໗ Burmese ၇

Digit at this position in famous constants

π — Pi (π): Digit 7 = 2
e — Euler's number (e): Digit 7 = 1
φ — Golden ratio (φ): Digit 7 = 3
√2 — Pythagoras's (√2): Digit 7 = 3
ln 2 — Natural log of 2: Digit 7 = 7
γ — Euler-Mascheroni (γ): Digit 7 = 5

Also seen as

Prime neighborhood

Adjacent primes:

Previous prime: 5 (gap of 2)
Next prime: 11 (gap of 4)

Pair status: twin with 5, cousin with 11.

ASCII character

As an ASCII codepoint, 7 is BEL (bell). ASCII control character.

Hex color

#000007

RGB(0, 0, 7)

IPv4 address

As an unsigned 32-bit integer, this is the IPv4 address 0.0.0.7.

Address: 0.0.0.7
Class: reserved
IPv4-mapped IPv6: ::ffff:0.0.0.7

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