18531721 has 8 divisors (see below), whose sum is σ = 20825280. Its totient is φ = 16362192.

The previous prime is 18531719. The next prime is 18531743. The reversal of 18531721 is 12713581.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 18531721 - 2¹ = 18531719 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18531721.

It is not an unprimeable number, because it can be changed into a prime (18531421) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 30691 + ... + 31288.

It is an arithmetic number, because the mean of its divisors is an integer number (2603160).

Almost surely, 2^18531721 is an apocalyptic number.

It is an amenable number.

18531721 is a deficient number, since it is larger than the sum of its proper divisors (2293559).

18531721 is a wasteful number, since it uses less digits than its factorization.

18531721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 62015.

The product of its digits is 1680, while the sum is 28.

The square root of 18531721 is about 4304.8485455356. The cubic root of 18531721 is about 264.6296999582.

The spelling of 18531721 in words is "eighteen million, five hundred thirty-one thousand, seven hundred twenty-one".