Primality
1 is by convention neither a prime number nor a composite number, but a unit (meaning of ring theory) like −1 and, in the Gaussian integers, i and −i. The fundamental theorem of arithmetic guarantees unique factorization over the integers only up to units. For example, 4 = 22, but if units are included, is also equal to, say, (−1)6 × 123 × 22, among infinitely many similar "factorizations". 1 appears to meet the naïve definition of a prime number, being evenly divisible only by 1 and itself (also 1). As such, some mathematicians considered it a prime number as late as the middle of the 20th century, but mathematical consensus has generally and since then universally been to exclude it for a variety of reasons (such as complicating the fundamental theorem of arithmetic and other theorems related to prime numbers). 1 is the only positive integer divisible by exactly one positive integer, whereas prime numbers are divisible by exactly two positive integers, composite numbers are divisible by more than two positive integers, and zero is divisible by all positive integers. Table of basic calculations
In technology
The resin identification code used in recycling to identify polyethylene terephthalate. The ITU country code for the North American Numbering Plan area, which includes the United States, Canada, and parts of the Caribbean. A binary code is a sequence of 1 and 0 that is used in computers for representing any kind of data. In many physical devices, 1 represents the value for "on", which means that electricity is flowing.
Addiction
Evidence to date does not support the efficacy for N-acetylcysteine in treating addictions to gambling, methamphetamine, or nicotine. Based upon limited evidence, NAC appears to normalize glutamate neurotransmission in the nucleus accumbens and other brain structures, in part by upregulating the expression of excitatory amino acid transporter 2 (EAAT2), a.k.a. glutamate transporter 1 (GLT1), in individuals with addiction. While NAC has been demonstrated to modulate glutamate neurotransmission in adult humans who are addicted to cocaine, NAC does not appear to modulate glutamate neurotransmission in healthy adult humans. NAC has been hypothesized to exert beneficial effects through its modulation of glutamate and dopamine neurotransmission as well as its antioxidant properties. Microbiological use
Acetylcysteine can be used in Petroffs method of liquefaction and decontamination of sputum, in preparation for recovery of mycobacterium. It also displays significant antiviral activity against the influenza A viruses.Acetylcysteine has bactericidal properties and breaks down bacterial biofilms of clinically relevant pathogens including Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis, Enterobacter cloacae, Staphylococcus epidermidis, and Klebsiella pneumoniae. Other uses
Acetylcysteine has been used to complex palladium, to help it dissolve in water. This helps to remove palladium from drugs or precursors synthesized by palladium-catalyzed coupling reactions. N-actelylcysteine can be used to protect the liver. Side effects
The most commonly reported adverse effects for IV formulations of acetylcysteine are rash, urticaria, and itchiness. Up to 18% of patients have been reported to experience anaphylaxis reaction, which are defined as rash, 
hypotension, wheezing, and/or shortness of breath. Lower rates of anaphylactoid reactions have been reported with slower rates of infusion.