28915921 has 4 divisors (see below), whose sum is σ = 28937200. Its totient is φ = 28894644.

The previous prime is 28915919. The next prime is 28915933. The reversal of 28915921 is 12951982.

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 a cyclic number.

It is not a de Polignac number, because 28915921 - 2¹ = 28915919 is a prime.

It is a super-2 number, since 2×28915921² = 1672260974556482, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28915721) 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, 8451 + ... + 11368.

It is an arithmetic number, because the mean of its divisors is an integer number (7234300).

Almost surely, 2^28915921 is an apocalyptic number.

It is an amenable number.

28915921 is a deficient number, since it is larger than the sum of its proper divisors (21279).

28915921 is a wasteful number, since it uses less digits than its factorization.

28915921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21278.

The product of its digits is 12960, while the sum is 37.

The square root of 28915921 is about 5377.3526014201. The cubic root of 28915921 is about 306.9344786908.

It can be divided in two parts, 289159 and 21, that added together give a triangular number (289180 = T₇₆₀).

The spelling of 28915921 in words is "twenty-eight million, nine hundred fifteen thousand, nine hundred twenty-one".