18855721 has 4 divisors (see below), whose sum is σ = 18993492. Its totient is φ = 18717952.

The previous prime is 18855709. The next prime is 18855731. The reversal of 18855721 is 12755881.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12755881 = 53 ⋅240677.

It can be written as a sum of positive squares in 2 ways, for example, as 14899600 + 3956121 = 3860^2 + 1989^2 .

It is a cyclic number.

It is not a de Polignac number, because 18855721 - 2⁵ = 18855689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18855701) 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, 68680 + ... + 68953.

It is an arithmetic number, because the mean of its divisors is an integer number (4748373).

Almost surely, 2^18855721 is an apocalyptic number.

It is an amenable number.

18855721 is a deficient number, since it is larger than the sum of its proper divisors (137771).

18855721 is a wasteful number, since it uses less digits than its factorization.

18855721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 137770.

The product of its digits is 22400, while the sum is 37.

The square root of 18855721 is about 4342.3174688178. The cubic root of 18855721 is about 266.1630193368.

The spelling of 18855721 in words is "eighteen million, eight hundred fifty-five thousand, seven hundred twenty-one".