28420921 has 4 divisors (see below), whose sum is σ = 29189092. Its totient is φ = 27652752.

The previous prime is 28420919. The next prime is 28420927. The reversal of 28420921 is 12902482.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 17131321 + 11289600 = 4139^2 + 3360^2 .

It is a cyclic number.

It is not a de Polignac number, because 28420921 - 2¹ = 28420919 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 28420921.

It is not an unprimeable number, because it can be changed into a prime (28420927) 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, 384030 + ... + 384103.

It is an arithmetic number, because the mean of its divisors is an integer number (7297273).

Almost surely, 2^28420921 is an apocalyptic number.

It is an amenable number.

28420921 is a deficient number, since it is larger than the sum of its proper divisors (768171).

28420921 is an equidigital number, since it uses as much as digits as its factorization.

28420921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 768170.

The product of its (nonzero) digits is 2304, while the sum is 28.

The square root of 28420921 is about 5331.1275542797. The cubic root of 28420921 is about 305.1729593216.

The spelling of 28420921 in words is "twenty-eight million, four hundred twenty thousand, nine hundred twenty-one".