Number reference
73 explained.
73: seventy-three, prime; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- seventy-three
- Classification
- prime
- Factors
- 1, 73
- Prime factorization
- 73
- Square root
- 8.544004
- Cube root
- 4.179339
- Binary
- 1001001
- Octal
- 111
- Hexadecimal
- 49
- Roman numeral
- LXXIII
- Digit sum
- 10
- Digital root
- 1
What makes 73 notable
- Prime. 73 is prime: it has exactly two divisors, 1 and itself, so it cannot be split into equal whole-number groups any other way.
73 in everyday use
Seventy-three is the atomic number of tantalum, the metal in the tiny capacitors inside mobile phones. In amateur radio "73" has meant "best regards" since the days of the telegraph. The number became a running joke on The Big Bang Theory, where Sheldon Cooper calls it the best number, and in 2019 two mathematicians proved that the properties he lists make 73 unique.
Seventy-three is the 21st prime, and its reversal, 37, is the 12th prime — while 21 is 7 × 3, the product of its digits. In binary it is 1001001, a palindrome. It is the sum of two squares, 64 + 9, and a twin prime with 71. It is also an emirp, one of the primes that stays prime when its digits are reversed.
Nearby numbers
How to read this page
Because 73 is prime, the factor list stops at 1 and 73 itself, so it cannot be shared into equal whole-number groups. That is also what makes it useful as a building block: every larger number with 73 in its prime factorisation inherits it from here.
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