28399721 has 4 divisors (see below), whose sum is σ = 32456832. Its totient is φ = 24342612.

The previous prime is 28399691. The next prime is 28399727. The reversal of 28399721 is 12799382.

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.

It is not a de Polignac number, because 28399721 - 2²² = 24205417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28399727) 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, 2028545 + ... + 2028558.

It is an arithmetic number, because the mean of its divisors is an integer number (8114208).

Almost surely, 2^28399721 is an apocalyptic number.

It is an amenable number.

28399721 is a deficient number, since it is larger than the sum of its proper divisors (4057111).

28399721 is an equidigital number, since it uses as much as digits as its factorization.

28399721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4057110.

The product of its digits is 54432, while the sum is 41.

The square root of 28399721 is about 5329.1388610169. The cubic root of 28399721 is about 305.0970612881.

The spelling of 28399721 in words is "twenty-eight million, three hundred ninety-nine thousand, seven hundred twenty-one".