| ||||
---|---|---|---|---|

Cardinal | seventy-three | |||

Ordinal | 73rd (seventy-third) | |||

Factorization | prime | |||

Prime | 21st | |||

Divisors | 1, 73 | |||

Greek numeral | ΟΓ´ | |||

Roman numeral | LXXIII | |||

Binary | 1001001_{2} | |||

Ternary | 2201_{3} | |||

Quaternary | 1021_{4} | |||

Quinary | 243_{5} | |||

Senary | 201_{6} | |||

Octal | 111_{8} | |||

Duodecimal | 61_{12} | |||

Hexadecimal | 49_{16} | |||

Vigesimal | 3D_{20} | |||

Base 36 | 21_{36} |

**73** (**seventy-three**) is the natural number following 72 and preceding 74. In English, it is the smallest natural number with twelve letters in its spelled out name.

## Contents

## In mathematics

**73** is:

- the 21st prime number. The previous is 71, with which it composes the 8th twin prime.
- a permutable prime with 37.
- a star number.
^{[1]} - the largest minimal Primitive root in the first 100,000 primes. In other words, if
*p*is one of the first 100,000 primes, then at least one of the primes 3, 5, 7, 11, 13, 17, ..., 73 is a primitive root modulo*p*. - the smallest prime congruent to 1 modulo 24.
- an emirp, meaning that the reverse of 73, that is, 37, is also a prime number.
^{[2]}73 is the 21st prime number while 37 is the 12th prime number. - the smallest prime with a composite sum of digits, in base 5.
- palindromic in bases 2 (1001001
_{2}) and 8 (111_{8}). - the only prime repunit in base 8 (111
_{8}). - the smallest factor of the first composite generalized Fermat number in base 10 (10
^{4}+ 1 = 10,001 = 73 × 137).

Also:

- The number 21 has prime factors 7 and 3. The number 21 in binary is 10101; 7 in binary is 111, 3 in binary is 11, and seventy-three in binary is 1001001. All of these are palindromes. In addition, of the
**7**binary digits representing 73, there are**3**ones. Also, 37 + 12 = 49 (seven squared) and 73 + 21 = 94 = 47 × 2, 47 + 2 also being equal to seven squared. Additionally, both 73 and its mirror, 37, are sexy primes twice over, as 31, 43, 67 and 79 are all prime numbers. - In addition to having prime factors 7 and 3, the number 21 represents the ternary (base-3) equivalent of the decimal numeral 7, or 21
_{3}= 7_{10}. - 7
^{3}= 343, a palindrome. Replacing the first two digits of 343 with their sum yields 73. - Every positive integer can be written as the sum of 73 or fewer sixth powers (see Waring's problem).

## In science

- The atomic number of tantalum

### In astronomy

- Messier object M73, a magnitude 9.0 apparent open cluster in the constellation Aquarius
- The New General Catalogue object NGC 73, a barred spiral galaxy in the constellation Cetus
- The number of seconds it took for the Space Shuttle Challenger OV-099 shuttle to explode after launch.
- 73 is the number of rows in the 1,679-bit Arecibo message, sent to space in search for extraterrestrial intelligence.

## In other fields

**73** is also:

- The number of days in 1/5 of a non-leap year.
- The year
**AD 73**, 73 BC, or 1973. - The number of books in the Catholic Bible.
^{[3]} - Amateur radio operators and other morse code users commonly use the number 73 as a "92 Code" abbreviation for "best regards", typically when ending a QSO (a conversation with another operator). These codes also facilitate communication between operators who may not be native English speakers. [1] In Morse code, 73 is an easily recognized palindrome - ( - - · · · · · · - - ).
*73*(also known as*73 Amateur Radio Today*), was an amateur radio magazine published from 1960 to 2003.- 73 was the number on the Torpedo Patrol (PT) boat in the TV show McHale's Navy
- The registry of the U.S. Navy's nuclear aircraft carrier USS George Washington (CVN-73), named after U.S. President George Washington.
*No. 73*was the name of a 1980s children's television programme in the United Kingdom. It ran from 1982–1988 and starred Sandi Toksvig- Pizza 73 is a Canadian pizza chain with 52 stores
- Game show Match Game '73 in 1973
- Fender Rhodes Stage 73 Piano
- Sonnet 73 by William Shakespeare
- The number of the French department Savoie
- On a CB radio, 10-73 means "speed trap at..."

## In sports

- In international curling competitions, each side is given 73 minutes to complete all of its throws.
- In baseball, the single-season home run record set by Barry Bonds in 2001.
- In basketball, the number of games the Golden State Warriors won in the 2015-16 season (73-9), the most wins in NBA history.
- NFL: In the 1940 NFL championship game, the Bears beat the Redskins 73–0, the largest score ever in an NFL game. (The Redskins won their previous regular season game, 7–3).

## See also

## References

**^**"Sloane's A003154 : Centered 12-gonal numbers. Also star numbers: 6*n*(n-1) + 1".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**"Sloane's A006567 : Emirps".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**"Catholic Bible 101".*Catholic Bible 101*. Retrieved 16 September 2018.