81728693 has 2 divisors, whose sum is σ = 81728694. Its totient is φ = 81728692.

The previous prime is 81728659. The next prime is 81728701. The reversal of 81728693 is 39682718.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 60871204 + 20857489 = 7802^2 + 4567^2 .

It is a cyclic number.

It is not a de Polignac number, because 81728693 - 2¹⁰ = 81727669 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81728653) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40864346 + 40864347.

It is an arithmetic number, because the mean of its divisors is an integer number (40864347).

Almost surely, 2^81728693 is an apocalyptic number.

It is an amenable number.

81728693 is a deficient number, since it is larger than the sum of its proper divisors (1).

81728693 is an equidigital number, since it uses as much as digits as its factorization.

81728693 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 145152, while the sum is 44.

The square root of 81728693 is about 9040.3923034346. The cubic root of 81728693 is about 433.9684776103.

The spelling of 81728693 in words is "eighty-one million, seven hundred twenty-eight thousand, six hundred ninety-three".