28813921 has 4 divisors (see below), whose sum is σ = 28829952. Its totient is φ = 28797892.

The previous prime is 28813919. The next prime is 28813931. The reversal of 28813921 is 12931882.

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: 12931882 = 2 ⋅6465941.

It is a cyclic number.

It is not a de Polignac number, because 28813921 - 2¹ = 28813919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28813901) 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, 4921 + ... + 9046.

It is an arithmetic number, because the mean of its divisors is an integer number (7207488).

Almost surely, 2^28813921 is an apocalyptic number.

It is an amenable number.

28813921 is a deficient number, since it is larger than the sum of its proper divisors (16031).

28813921 is a wasteful number, since it uses less digits than its factorization.

28813921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16030.

The product of its digits is 6912, while the sum is 34.

The square root of 28813921 is about 5367.8600019002. The cubic root of 28813921 is about 306.5731529354.

The spelling of 28813921 in words is "twenty-eight million, eight hundred thirteen thousand, nine hundred twenty-one".