19 (number)
19 (nineteen) is the natural number following 18 and preceding 20.
| Template:Numbers 10s | |
| Cardinal | nineteen |
| Ordinal | nineteenth |
| Factorization | prime |
| Divisors | 1, 19 |
| Roman numeral | XIX |
| Binary | 10011 |
| Hexadecimal | 13 |
In mathematics
Nineteen is the 8th smallest prime number. The sequence continues 23, 29, 31, 37... 19 is the seventh Mersenne prime exponent.
It is also a Keith number, because it recurs in a Fibonacci-like sequence started from its base 10 digits: 1, 9, 10, 19...
With respect to divisibility, nineteen has a very simple test: 19 divides 100×a+b if and only if it divides a+4×b.
Nineteen is a centered triangular number, centered hexagonal number, and an octahedral number.
Every positive integer is the sum of at most nineteen fourth powers.
The decimal expansion of 1/19 has a period of maximum length: 18 digits.
Nineteen is a Heegner number.
In music
"19" is a 1985 hit song by Paul Hardcastle, with a strong anti-war message, based on 19 being the average age of soldiers in the Vietnam war.
Other songs with the number in their titles include "Nineteen" by the Old 97's and "Hey, Nineteen" by Steely Dan.
In other fields
Nineteen is
- The atomic number of potassium.
- The nineteenth state to enter the Union was Indiana.
- part of the name of a breakfast cereal: Product 19.
- The Soviet submarine K-19 was the first Soviet nuclear ballistic submarine
- I-19 is the designation for a US interstate highway in Arizona.
- 19 years is very close to 235 lunations. See Metonic cycle.
- Historical years: 19 A.D., 19 B.C., or 1919
- A significant recurring number in the Dark Tower novels by author Stephen King.
- The number of angels guarding Hell according to the Qur'an: "Upon it is nineteen" (74:30)
- The number of surat Maryam in the Qur'an
- The number of letters in the basmala formula "In the Name of God, the Merciful, the Compassionate" in Arabic
- A key number in the unorthodox theories of Rashad Khalifa about the Qur'an
- In golf the 19th hole is the clubhouse bar