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| 19 | |
|---|---|
| Cardinal | nineteen |
| Ordinal | 19th (nineteenth) |
| Numeral system | nonadecimal |
| Factorization | prime |
| Divisors | 1, 19 |
| Roman numeral | XIX |
| Binary | 100112 |
| Octal | 238 |
| Duodecimal | 1712 |
| Hexadecimal | 1316 |
19 (nineteen) is the natural number following 18 and preceding 20. It is a prime number.
In English speech, the numbers 19 and 90 are often confused, as sounding very similar. When carefully enunciated, they differ in which syllable is stressed: 19 /naɪnˈtiːn/ vs 90 /ˈnaɪnti/. However, in dates such as 1999, and when contrasting numbers in the teens and when counting, such as 17, 18, 19, the stress shifts to the first syllable: 19 /ˈnaɪntiːn/.
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19 is the 8th smallest prime number. The sequence continues 23, 29, 31, 37...
19 is the seventh Mersenne prime exponent.
19 is the aliquot sum of two odd discrete semiprimes, 65 and 77 and is the base of the 19-aliquot tree.
19 is a centered triangular number, centered hexagonal number and a Heegner number.
You can make the number 19 by adding or subtracting but not multiplying (whole numbers), 19 can also be made by division.
The only non-trivial normal magic hexagon contains 19 hexagons (the other being 1).
19 is the first number with more than one digit that can be written from base 2 to base 19 using only the digits 0 to 9; the other number is 20.[1]
In the Bábí and Bahá'í faiths, a group of 19 is called a Váhid, a Unity (Arabic: واحد wāhid, "one"). The numerical value of this word in the Abjad numeral system is 19.
A.D. 19, 19 B.C., 1919, 2019, etc.
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