28223721 has 24 divisors (see below), whose sum is σ = 44509920. Its totient is φ = 17822592.

The previous prime is 28223717. The next prime is 28223731. The reversal of 28223721 is 12732282.

It is a happy number.

It is not a de Polignac number, because 28223721 - 2² = 28223717 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28223731) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1561 + ... + 7673.

It is an arithmetic number, because the mean of its divisors is an integer number (1854580).

Almost surely, 2^28223721 is an apocalyptic number.

It is an amenable number.

28223721 is a deficient number, since it is larger than the sum of its proper divisors (16286199).

28223721 is an equidigital number, since it uses as much as digits as its factorization.

28223721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6147 (or 6135 counting only the distinct ones).

The product of its digits is 2688, while the sum is 27.

The square root of 28223721 is about 5312.6002108196. The cubic root of 28223721 is about 304.4655011997.

The spelling of 28223721 in words is "twenty-eight million, two hundred twenty-three thousand, seven hundred twenty-one".