273 (number)

273 is a sphenic number, being the product of three distinct primes: 3 × 7 × 13.^[1] It is also a lucky number,^[2] a truncated triangular pyramid number,^[3] and an idoneal number.^[4]

There are 273 different ternary trees with five nodes.^[5] It is in the Moser–de Bruijn sequence, comprising the sum 4⁴ + 4² + 4⁰ = 256 + 16 + 1,^[6] and is a central polygonal number.^[7]

273 is a deficient number, as the sum of its proper divisors (175) is less than itself.

The number 273 has particular significance in temperature measurement. Absolute zero, the lowest possible temperature, is −273.15 °C (0.00 K; −459.67 °F), often rounded to −273 °C.^[8] Correspondingly, the freezing point of water at standard pressure is approximately 273 K (273.15 K exactly).^[8]

This relationship arises from Charles's law, which determined that at constant pressure, ideal gases expand or contract their volume by about 1⁄273 per degree Celsius of temperature change.^[9]

• 273 Atropos is a main-belt asteroid discovered by Austrian astronomer Johann Palisa on 8 March 1888 in Vienna. It is named after Atropos, one of the Three Fates in Greek mythology.^[10]
• NGC 273 is an edge-on lenticular galaxy in the constellation Cetus, discovered on 10 September 1785 by William Herschel.^[11]