19,991
19,991 is a prime, odd.
19,991 (nineteen thousand nine hundred ninety-one) is an odd 5-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 hexadecimal, 0x4E17.
Interestingness
Properties
Primality
19,991 is prime. It has exactly two divisors: 1 and itself.
Divisors & multiples
Sums & aliquot sequence
Continued fraction of √n
√19,991 = [141; (2, 1, 1, 3, 4, 1, 1, 16, 12, 4, 3, 1, 2, 1, 4, 2, 2, 5, 4, 28, 25, 1, 2, 21, …)]
Representations
- In words
- nineteen thousand nine hundred ninety-one
- Ordinal
- 19991st
- Binary
- 100111000010111
- Octal
- 47027
- Hexadecimal
- 0x4E17
- Base64
- Thc=
- One's complement
- 45,544 (16-bit)
- Scientific notation
- 1.9991 × 10⁴
- As a duration
- 19,991 s = 5 hours, 33 minutes, 11 seconds
As an angle
Historical numeral systems
- Babylonian (base 60)
- 𒁹𒁹𒁹𒁹𒁹 𒌋𒌋𒌋𒁹𒁹𒁹 𒌋𒁹
- Egyptian hieroglyphic
- 𓂍𓆼𓆼𓆼𓆼𓆼𓆼𓆼𓆼𓆼𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓍢𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓎆𓏺
- Greek (Milesian)
- ͵ιθϡϟαʹ
- Mayan (base 20)
- 𝋢·𝋩·𝋳·𝋫
- Chinese
- 一萬九千九百九十一
- Chinese (financial)
- 壹萬玖仟玖佰玖拾壹
Digit at this position in famous constants
- π — Pi (π)
- Digit 19,991 = 4
- e — Euler's number (e)
- Digit 19,991 = 2
- φ — Golden ratio (φ)
- Digit 19,991 = 6
- √2 — Pythagoras's (√2)
- Digit 19,991 = 6
- ln 2 — Natural log of 2
- Digit 19,991 = 7
- γ — Euler-Mascheroni (γ)
- Digit 19,991 = 1
Also seen as
UTF-8 encoding: E4 B8 97 (3 bytes).
As an unsigned 32-bit integer, this is the IPv4 address 0.0.78.23.
- Address
- 0.0.78.23
- Class
- reserved
- IPv4-mapped IPv6
- ::ffff:0.0.78.23
Unspecified address (0.0.0.0/8) — "this network" placeholder.
Heard as a frequency, 19,991 Hz is closest to:
- Concert pitch (A4 = 440 Hz): D♯10 (19912.1 Hz, +7¢)
- Scientific pitch (C4 = 256 Hz): D♯10 (19484 Hz, +44¢)
- Baroque pitch (A4 = 415 Hz): E10 (19897.5 Hz, +8¢)
The digit sequence 19991 first appears in π at position 42,058 of the decimal expansion (the 42,058ordinal-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
- 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.