• 73 can be written using four 4's:

• Deleting all the even digits from 2^{73} = 9444732965739290427392 we obtain a prime (973957399739).

73 has 2 divisors, whose sum is σ = 74. Its totient is φ = 72.

The previous prime is 71. The next prime is 79. The reversal of 73 is 37.

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.

It can be written as a sum of positive squares in only one way, i.e., 64 + 9 = 8^2 + 3^2 .

73 is a truncatable prime.

It is an emirp because it is prime and its reverse (37) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 73 - 2^{1} = 71 is a prime.

Together with 71, it forms a pair of twin primes.

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 a nontrivial repunit in base 8.

It is a pernicious number, because its binary representation contains a prime number (3) of ones.

It is an upside-down number.

It is a Pierpont prime, being equal to 2^{3} ⋅ 3^{2} + 1.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 36 + 37.

It is an arithmetic number, because the mean of its divisors is an integer number (37).

It is an amenable number.

73 is a deficient number, since it is larger than the sum of its proper divisors (1).

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 product of its digits is 21, while the sum is 10.

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 = T_{8}).

Multiplying 73 by its reverse (37), we get a triangular number (2701 = T_{73}).

The spelling of 73 in words is "seventy-three", and thus it is an aban number, an iban number, an oban number, and an uban number.

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