28732721 has 4 divisors (see below), whose sum is σ = 28743744. Its totient is φ = 28721700.

The previous prime is 28732709. The next prime is 28732741. The reversal of 28732721 is 12723782.

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 a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 28732721 - 2⁶ = 28732657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28732741) 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, 836 + ... + 7626.

It is an arithmetic number, because the mean of its divisors is an integer number (7185936).

Almost surely, 2^28732721 is an apocalyptic number.

It is an amenable number.

28732721 is a deficient number, since it is larger than the sum of its proper divisors (11023).

28732721 is an equidigital number, since it uses as much as digits as its factorization.

28732721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11022.

The product of its digits is 9408, while the sum is 32.

The square root of 28732721 is about 5360.2911301533. The cubic root of 28732721 is about 306.2848992021.

The spelling of 28732721 in words is "twenty-eight million, seven hundred thirty-two thousand, seven hundred twenty-one".