28121665 has 32 divisors (see below), whose sum is σ = 40755456. Its totient is φ = 18351360.

The previous prime is 28121657. The next prime is 28121707. The reversal of 28121665 is 56612182.

It is not a de Polignac number, because 28121665 - 2³ = 28121657 is a prime.

It is a Smith number, since the sum of its digits (31) 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 an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 25924 + ... + 26986.

It is an arithmetic number, because the mean of its divisors is an integer number (1273608).

Almost surely, 2^28121665 is an apocalyptic number.

It is an amenable number.

28121665 is a deficient number, since it is larger than the sum of its proper divisors (12633791).

28121665 is a wasteful number, since it uses less digits than its factorization.

28121665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1129.

The product of its digits is 5760, while the sum is 31.

The square root of 28121665 is about 5302.9864227622. The cubic root of 28121665 is about 304.0980790703.

The spelling of 28121665 in words is "twenty-eight million, one hundred twenty-one thousand, six hundred sixty-five".