Seventythree

Seventythree is the natural number that follows seventy-two and precedes seventy-four. In mathematics, it is a prime number and is used in studies of prime distribution, numeral bases, and integer sequences.

Seventythree is the 21st prime number. In binary, it is written as 1001001, which is a palindrome. As a prime whose reversal is a different prime, it is classified as an emirp (73 reversed is 37, also prime). Its digits sum to 10, and their product is 21.

In science and technology, the number 73 is the atomic number of tantalum (Ta), a transition metal valued for its corrosion resistance and high melting point. Tantalum is widely used in electronic capacitors and specialty alloys.

In popular culture, 73 is sometimes cited as a mathematically interesting number. For instance, in The Big Bang Theory, the character Sheldon Cooper calls 73 "the best number" because its binary representation reads the same forwards and backwards and its position as the 21st prime.

Calendar-wise, the 73rd day of the year falls on March 14 in common years and March 13 in leap years.