253

253 is the natural number that comes after 252 and before 254. In mathematics, it is an odd composite number with prime factorization 11 × 23, making it a semiprime. Its divisors are 1, 11, 23, and 253; the sum of its proper divisors is 35, so 253 is deficient. In various numeral systems it can be written as 253 in decimal, 11111101 in binary, 375 in octal, and FD in hexadecimal. The Roman numeral representation is CCLIII. The digits sum to 10, and several modular and divisibility properties can be derived from its factors.

In geography and telecommunications, 253 is used as an area code in the United States, covering parts of western Washington state, including the city of Tacoma and surrounding areas. It was created in 1997 in a split from area code 206. Area code 253 is part of the North American Numbering Plan and may be complemented by an overlay or reallocation in its region over time.

In science and astronomy, 253 appears in notable contexts. NGC 253, also known as the Sculptor Galaxy, is a bright, nearby spiral galaxy in the constellation Sculptor. It is a starburst galaxy about 11 million to 12 million light-years away and is frequently studied in infrared and radio wavelengths. In physics and engineering, the 253.7 nanometer emission line of mercury is a well-known UV-C line used in germicidal lamps for disinfection.

Other uses of the number 253 are occasional references in catalog numbers, model numbers, and route indices, but the primary associations lie in mathematics, telecommunications, and astronomy.