18688921 has 4 divisors (see below), whose sum is σ = 18814500. Its totient is φ = 18563344.

The previous prime is 18688909. The next prime is 18688927. The reversal of 18688921 is 12988681.

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 2975625 + 15713296 = 1725^2 + 3964^2 .

It is a cyclic number.

It is not a de Polignac number, because 18688921 - 2¹¹ = 18686873 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18688927) 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, 62566 + ... + 62863.

It is an arithmetic number, because the mean of its divisors is an integer number (4703625).

Almost surely, 2^18688921 is an apocalyptic number.

It is an amenable number.

18688921 is a deficient number, since it is larger than the sum of its proper divisors (125579).

18688921 is a wasteful number, since it uses less digits than its factorization.

18688921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 125578.

The product of its digits is 55296, while the sum is 43.

The square root of 18688921 is about 4323.0684704270. The cubic root of 18688921 is about 265.3758568343.

The spelling of 18688921 in words is "eighteen million, six hundred eighty-eight thousand, nine hundred twenty-one".