28531721 has 4 divisors (see below), whose sum is σ = 28808832. Its totient is φ = 28254612.

The previous prime is 28531717. The next prime is 28531733. The reversal of 28531721 is 12713582.

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.

It is a cyclic number.

It is not a de Polignac number, because 28531721 - 2² = 28531717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28531781) 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, 138401 + ... + 138606.

It is an arithmetic number, because the mean of its divisors is an integer number (7202208).

Almost surely, 2^28531721 is an apocalyptic number.

It is an amenable number.

28531721 is a deficient number, since it is larger than the sum of its proper divisors (277111).

28531721 is a wasteful number, since it uses less digits than its factorization.

28531721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 277110.

The product of its digits is 3360, while the sum is 29.

The square root of 28531721 is about 5341.5092436502. The cubic root of 28531721 is about 305.5690210607.

The spelling of 28531721 in words is "twenty-eight million, five hundred thirty-one thousand, seven hundred twenty-one".