127 (number)

127 (one hundred [and] twenty-seven) is the natural number following 126 and preceding 128. It is also a prime number.

In mathematics

 * As a Mersenne prime, 127 is related to the perfect number 8128. 127 is also the largest known Mersenne prime exponent for a Mersenne number, $$2^{127}-1$$, which is also a Mersenne prime. It was discovered by Édouard Lucas in 1876 and held the record for the largest known prime for 75 years.
 * $$2^{127}-1$$ is the largest prime ever discovered by hand calculations as well as the largest known double Mersenne prime.
 * Furthermore, 127 is equal to $$2^{7}-1$$, and 7 is equal to $$2^{3}-1$$, and 3 is the smallest Mersenne prime, making 7 the smallest double Mersenne prime and 127 the smallest triple Mersenne prime.
 * There are a total of 127 prime numbers between 2,000 and 3,000.
 * 127 is also a cuban prime of the form $$p=\frac{x^{3}-y^{3}}{x-y}$$, $$x=y+1$$. The next prime is 131, with which it comprises a cousin prime. Because the next odd number, 129, is a semiprime, 127 is a Chen prime. 127 is greater than the arithmetic mean of its two neighboring primes; thus, it is a strong prime.
 * 127 is a centered hexagonal number.
 * It is the seventh Motzkin number.
 * 127 is a palindromic prime in nonary and binary.
 * 127 is the first Friedman prime in decimal. It is also the first nice Friedman number in decimal, since $$127=2^{7}-1 \,$$, as well as binary since $$1111111 = (1 + 1)^{111} - 1 \,$$.
 * 127 is the sum of the sums of the divisors of the first twelve positive integers.
 * 127 is the smallest prime that can be written as the sum of the first two or more odd primes: $$127 = 3 + 5 + 7 + 11 + 13 + 17 + 19 + 23 + 29$$.
 * 127 is the smallest odd number that cannot be written in the form $$p+2^{x}$$, for $p$ is a prime number, and $x$ is an integer, since $$127 - 2^0=126,$$ $$127 - 2^1=125,$$ $$127 - 2^2=123,$$ $$127 - 2^3=119,$$ $$127 - 2^4=111,$$ $$127 - 2^5=95,$$ and $$127 - 2^6=63$$ are all composite numbers.
 * 127 is an isolated prime where neither $$p-2$$ nor $$p+2$$ is prime.
 * 127 is the smallest digitally delicate prime in binary.
 * 127 is the 31st prime number and therefore it is the smallest Mersenne prime with a Mersenne prime index.
 * 127 is the largest number with the property $$127 = 1\cdot\textrm{prime}(1) + 2\cdot\textrm{prime}(2) + 7\cdot\textrm{prime}(7),$$ where $$\textrm{prime}(n)$$ is the $n$th prime number. There are only two numbers with that property; the other one is 43.
 * 127 is equal to $$\textrm{prime}^{6}(1),$$ where $$\textrm{prime}(n)$$ is the $n$th prime number.
 * 127 is the number of non-equivalent ways of expressing 10,000 as the sum of two prime numbers
 * 127/50 = 2.54, the number of centimeters in one inch.

In the military

 * USNS Mission San Luis Obispo (T-AO-127) was a Mission Buenaventura-class fleet oilers during World War II
 * USS Admiral W. S. Sims (AP-127) was a United States Navy transport ship
 * USS Allendale (APA-127) was a United States Navy Haskell-class attack transport
 * USS Alnitah (AK-127) was a United States Navy Crater-class cargo ship in World War II
 * USS Raccoon (IX-127) was a United States Navy Armadillo-class tanker
 * USS Tumult (AM-127) was a United States Navy Auk-class minesweeper for removing naval mines

In religion

 * The biblical figure Sarah died at the age of 127.
 * According to the Book of Esther, the Persian Empire under Ahasuerus consisted of 127 provinces "from India to Ethiopia".
 * Havamal Stanza 127 is used as a declaration against folkish traditions of Heathenry and specifically the Asatru Folk Assembly.

In transportation

 * The small Fiat 127 automobile
 * London Buses route 127 is a Transport for London contracted bus route in London
 * 127 is the number of many roads, including U.S. Route 127
 * STS-127 was a Space Shuttle Endeavour mission to the International Space Station which launched on June 15, 2009

In other fields

 * 127 Hours is a film released in 2010
 * The year AD 127 or 127 BC
 * 127 AH is a year in the Islamic calendar that corresponds to 744 – 745 CE
 * 127 Johanna, a Main belt asteroid
 * 127 film, a film format
 * The atomic number of Unbiseptium, an element that has not yet been discovered
 * The LZ 127 Graf Zeppelin, a dirigible
 * Sonnet 127 by William Shakespeare
 * 127th Street Ensemble was a troupe of African-American actors which included Tupac Amaru Shakur
 * NCT 127, K-pop boy group under SM Entertainment
 * In IP (Internet Protocol) Version 4, it is the last Class A network and is also the subnet used for loopback functionality in computer networking
 * The highest signed 8-bit integer, using two's complement
 * The non-printable "Delete" (DEL) control character in ASCII.
 * Linotype (and Intertype) machines used brass matrices with one of 127 possible combinations punched into the top to enable the matrices to return to their proper channel in the magazine.
 * 127 is the smallest positive integer, n, such that n centimeters is a whole number of inches. 127 cm is exactly 50 inches.
 * 127 is the total number of people, including self and all ancestors, in a 7-generation (back to 4-great grandparents) pedigree chart in genealogy.