- 73 is an odd prime number and a permutable prime.
- 73 is the 4th smallest star number, a number expressed with 6n(n − 1) + 1 for a positive integer n.
- It is one of only four known Mersenne–Fermat primes, which are neither Fermat nor Mersenne primes.
In Greek-based number-naming systems, 73 is associated with prefix "triaheptaconta-", and with prefix "treseptuaginti-" in Latin systems.
- MathWorld, Star Number