1728721 has 4 divisors (see below), whose sum is σ = 1736500. Its totient is φ = 1720944.

The previous prime is 1728697. The next prime is 1728733. The reversal of 1728721 is 1278271.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1535121 + 193600 = 1239^2 + 440^2 .

It is a cyclic number.

It is not a de Polignac number, because 1728721 - 2⁵ = 1728689 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1728721.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1728761) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3546 + ... + 4003.

It is an arithmetic number, because the mean of its divisors is an integer number (434125).

2^1728721 is an apocalyptic number.

It is an amenable number.

1728721 is a deficient number, since it is larger than the sum of its proper divisors (7779).

1728721 is an equidigital number, since it uses as much as digits as its factorization.

1728721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7778.

The product of its digits is 1568, while the sum is 28.

The square root of 1728721 is about 1314.8083510535. The cubic root of 1728721 is about 120.0166874941.

The spelling of 1728721 in words is "one million, seven hundred twenty-eight thousand, seven hundred twenty-one".