18707221 has 4 divisors (see below), whose sum is σ = 20146252. Its totient is φ = 17268192.

The previous prime is 18707219. The next prime is 18707231. The reversal of 18707221 is 12270781.

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 1782225 + 16924996 = 1335^2 + 4114^2 .

It is a cyclic number.

It is not a de Polignac number, because 18707221 - 2¹ = 18707219 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 18707221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18707201) 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, 719496 + ... + 719521.

It is an arithmetic number, because the mean of its divisors is an integer number (5036563).

Almost surely, 2^18707221 is an apocalyptic number.

It is an amenable number.

18707221 is a deficient number, since it is larger than the sum of its proper divisors (1439031).

18707221 is a wasteful number, since it uses less digits than its factorization.

18707221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1439030.

The product of its (nonzero) digits is 1568, while the sum is 28.

The square root of 18707221 is about 4325.1845047350. The cubic root of 18707221 is about 265.4624463514.

The spelling of 18707221 in words is "eighteen million, seven hundred seven thousand, two hundred twenty-one".