• 73 can be written using four 4's:
• Deleting all the even digits from 273 = 9444732965739290427392 we obtain a prime (973957399739).
73 is nontrivially palindromic in base 2 and base 8.
It is the 4-th star number.
73 is an esthetic number in base 11, because in such base its adjacent digits differ by 1.
It is a weak prime.
73 is a truncatable prime.
It is a cyclic number.
It is the 9-th Hogben number.
73 is a lucky number.
73 is a nontrivial repdigit in base 8.
It is a plaindrome in base 7, base 8, base 11, base 13, base 15 and base 16.
It is a nialpdrome in base 8, base 9, base 10, base 12 and base 14.
It is a zygodrome in base 8.
It is a panconsummate number.
It is an upside-down number.
It is a Pierpont prime, being equal to 23 ⋅ 32 + 1.
It is an amenable number.
73 is an equidigital number, since it uses as much as digits as its factorization.
73 is an odious number, because the sum of its binary digits is odd.
The square root of 73 is about 8.5440037453. The cubic root of 73 is about 4.1793391964.
Subtracting from 73 its reverse (37), we obtain a triangular number (36 = T8).
Multiplying 73 by its reverse (37), we get a triangular number (2701 = T73).