28009921 has 4 divisors (see below), whose sum is σ = 28105812. Its totient is φ = 27914032.

The previous prime is 28009913. The next prime is 28009937. The reversal of 28009921 is 12990082.

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 11696400 + 16313521 = 3420^2 + 4039^2 .

It is a cyclic number.

It is not a de Polignac number, because 28009921 - 2³ = 28009913 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28009901) 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, 47506 + ... + 48091.

It is an arithmetic number, because the mean of its divisors is an integer number (7026453).

Almost surely, 2^28009921 is an apocalyptic number.

It is an amenable number.

28009921 is a deficient number, since it is larger than the sum of its proper divisors (95891).

28009921 is an equidigital number, since it uses as much as digits as its factorization.

28009921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 95890.

The product of its (nonzero) digits is 2592, while the sum is 31.

The square root of 28009921 is about 5292.4399854887. The cubic root of 28009921 is about 303.6947572373.

It can be divided in two parts, 2800 and 9921, that added together give a palindrome (12721).

The spelling of 28009921 in words is "twenty-eight million, nine thousand, nine hundred twenty-one".