15728721 has 4 divisors (see below), whose sum is σ = 20971632. Its totient is φ = 10485812.

The previous prime is 15728717. The next prime is 15728729. The reversal of 15728721 is 12782751.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12782751 = 3 ⋅4260917.

It is a cyclic number.

It is not a de Polignac number, because 15728721 - 2² = 15728717 is a prime.

It is not an unprimeable number, because it can be changed into a prime (15728729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2621451 + ... + 2621456.

It is an arithmetic number, because the mean of its divisors is an integer number (5242908).

Almost surely, 2^15728721 is an apocalyptic number.

It is an amenable number.

15728721 is a deficient number, since it is larger than the sum of its proper divisors (5242911).

15728721 is an equidigital number, since it uses as much as digits as its factorization.

15728721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5242910.

The product of its digits is 7840, while the sum is 33.

The square root of 15728721 is about 3965.9451584711. The cubic root of 15728721 is about 250.5519591343.

The spelling of 15728721 in words is "fifteen million, seven hundred twenty-eight thousand, seven hundred twenty-one".