73

73 is the natural number that follows 72 and precedes 74. In mathematics, it is a prime number, the 21st prime, and it has no divisors other than 1 and itself. Its decimal digits 7 and 3 form a pair whose reversal yields 37, another prime; notably, its binary representation is a palindrome: 1001001. In popular culture, The Big Bang Theory popularized the notion that 73 is the “best” number because of its prime position and its binary palindrome, a claim presented in a humorous, fictional context.

In science, 73 is the atomic number of tantalum (symbol Ta), a dense, corrosion-resistant transition metal used extensively in electronics, especially tantalum capacitors. Tantalum was named after Tantalus in Greek myth and was identified as an element in the early 19th century, with Anders Gustaf Ekeberg credited for its isolation in 1802.

Astronomically, Messier 73 (M73) is a star grouping in the southern constellation Puppis that is commonly described as an asterism rather than a true open cluster.

Historically, the year 73 CE is noted for events in the Roman Empire, including the fall of Masada after a prolonged siege. In numerals, 73 is written as LXXIII. In data encoding, the decimal value 73 corresponds to the ASCII code for the uppercase letter I, and 73 in octal is 111. The 73rd day of a common year is March 14, known to some as Pi Day.