21,808
21,808 is a composite number, even.
21,808 (twenty-one thousand eight hundred eight) is an even 5-digit number. It is a composite number with 20 divisors, and factors as 2⁴ × 29 × 47. Its proper divisors sum to 22,832, more than the number itself, making it an abundant number. Written other ways, in hexadecimal, 0x5530.
Interestingness
Properties
- Parity
- Even
- Digit count
- 5
- Digit sum
- 19
- Digit product
- 0
- Digital root
- 1
- Palindrome
- No
- Bit width
- 15 bits
- Reversed
- 80,812
- Recamán's sequence
- a(40,223) = 21,808
- Square (n²)
- 475,588,864
- Cube (n³)
- 10,371,641,946,112
- Divisor count
- 20
- σ(n) — sum of divisors
- 44,640
- φ(n) — Euler's totient
- 10,304
- Sum of prime factors
- 84
Primality
Prime factorization: 2 4 × 29 × 47
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√21,808 = [147; (1, 2, 12, 1, 1, 32, 3, 2, 1, 2, 1, 17, 1, 2, 1, 2, 3, 32, 1, 1, 12, 2, 1, 294)]
Period length 24 — the block in parentheses repeats forever.
Representations
- In words
- twenty-one thousand eight hundred eight
- Ordinal
- 21808th
- Binary
- 101010100110000
- Octal
- 52460
- Hexadecimal
- 0x5530
- Base64
- VTA=
- One's complement
- 43,727 (16-bit)
- Scientific notation
- 2.1808 × 10⁴
- As a duration
- 21,808 s = 6 hours, 3 minutes, 28 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒁹𒁹𒁹𒁹𒁹𒁹 𒁹𒁹𒁹 𒌋𒌋𒁹𒁹𒁹𒁹𒁹𒁹𒁹𒁹
- Egyptian hieroglyphic
- 𓂍𓂍𓆼𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓏺𓏺𓏺𓏺𓏺𓏺𓏺𓏺
- Greek (Milesian)
- ͵καωηʹ
- Mayan (base 20)
- 𝋢·𝋮·𝋪·𝋨
- Chinese
- 二萬一千八百零八
- Chinese (financial)
- 貳萬壹仟捌佰零捌
Digit at this position in famous constants
- π — Pi (π)
- Digit 21,808 = 4
- e — Euler's number (e)
- Digit 21,808 = 4
- φ — Golden ratio (φ)
- Digit 21,808 = 6
- √2 — Pythagoras's (√2)
- Digit 21,808 = 8
- ln 2 — Natural log of 2
- Digit 21,808 = 3
- γ — Euler-Mascheroni (γ)
- Digit 21,808 = 5
Also seen as
Goldbach's conjecture says every even integer greater than 2 is the sum of two primes. For 21808, here are decompositions:
- 5 + 21803 = 21808
- 41 + 21767 = 21808
- 71 + 21737 = 21808
- 107 + 21701 = 21808
- 191 + 21617 = 21808
- 197 + 21611 = 21808
- 239 + 21569 = 21808
- 251 + 21557 = 21808
Showing the first eight; more decompositions exist.
UTF-8 encoding: E5 94 B0 (3 bytes).
As an unsigned 32-bit integer, this is the IPv4 address 0.0.85.48.
- Address
- 0.0.85.48
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.85.48
Unspecified address (0.0.0.0/8) — "this network" placeholder.
The digit sequence 21808 first appears in π at position 90,304 of the decimal expansion (the 90,304ordinal-suffix:th digit after the integer 3).
Search range: the first 1,000,000 fractional digits of π. Any 6-digit-or-shorter string is virtually guaranteed to appear in there — the more interesting signal is the position.
Related reading
- Egyptian hieroglyphic numerals — Seven hieroglyphs for every power of ten, from a single stroke to a million.