28635721 has 4 divisors (see below), whose sum is σ = 29301712. Its totient is φ = 27969732.

The previous prime is 28635689. The next prime is 28635781. The reversal of 28635721 is 12753682.

It is a happy number.

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: 12753682 = 2 ⋅6376841.

It is a cyclic number.

It is not a de Polignac number, because 28635721 - 2⁵ = 28635689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28635781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 332931 + ... + 333016.

It is an arithmetic number, because the mean of its divisors is an integer number (7325428).

Almost surely, 2^28635721 is an apocalyptic number.

It is an amenable number.

28635721 is a deficient number, since it is larger than the sum of its proper divisors (665991).

28635721 is an equidigital number, since it uses as much as digits as its factorization.

28635721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 665990.

The product of its digits is 20160, while the sum is 34.

The square root of 28635721 is about 5351.2354648249. The cubic root of 28635721 is about 305.9398439283.

The spelling of 28635721 in words is "twenty-eight million, six hundred thirty-five thousand, seven hundred twenty-one".