28981921 has 4 divisors (see below), whose sum is σ = 29473200. Its totient is φ = 28490644.

The previous prime is 28981907. The next prime is 28981943. The reversal of 28981921 is 12918982.

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: 12918982 = 2 ⋅6459491.

It is a cyclic number.

It is not a de Polignac number, because 28981921 - 2⁹ = 28981409 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28981021) 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, 245551 + ... + 245668.

It is an arithmetic number, because the mean of its divisors is an integer number (7368300).

Almost surely, 2^28981921 is an apocalyptic number.

It is an amenable number.

28981921 is a deficient number, since it is larger than the sum of its proper divisors (491279).

28981921 is an equidigital number, since it uses as much as digits as its factorization.

28981921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 491278.

The product of its digits is 20736, while the sum is 40.

The square root of 28981921 is about 5383.4859524290. The cubic root of 28981921 is about 307.1678251407.

The spelling of 28981921 in words is "twenty-eight million, nine hundred eighty-one thousand, nine hundred twenty-one".