73
73 is a prime number — the 21st prime — and the atomic number of tantalum.
- Odd
- Prime
Where 73 fits
Why 73 is special
73's mirror number, 37, is the 12th prime — and 21 reversed is 12, a genuine, verifiable pattern that made 73 an internet-famous 'best number' after being popularised by the sitcom The Big Bang Theory.
73 is part of
Factors & digit properties
- Divisors (2)
- 1, 73
- Prime factorisation
- 73
- Digit sum
- 10
- Digital root
- 1
Representations
- Decimal
- 73
- Binary
- 1001001
- Octal
- 111
- Hexadecimal
- 49
- Roman numeral
- LXXIII
- Scientific notation
- 7.300 × 10^1
Other mathematical patterns
- Deficient number
- Lucky number (mathematical sieve)
- Twin prime
Related numbers & connections
71 and 73 are twin primes — two primes exactly two apart.
View 71 →Shares a distinctive class
- is associated with71
why?
Strength 0.50, confidence "high".
Science
73 is the atomic number of tantalum.
DocumentedScience
Mathematics
73 is prime and the 21st prime number; its mirror, 37, is prime and the 12th prime number — and 21 reversed is 12, a genuine, verifiable pattern popularised (including by the sitcom The Big Bang Theory) as 'the best number'.
DocumentedMathematics
Common questions
Is 73 a prime number?
Yes, 73 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 73?
The factors of 73 are 1, 73.
What is 73 in Roman numerals?
73 in Roman numerals is LXXIII.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026