18721609 has 8 divisors (see below), whose sum is σ = 19828800. Its totient is φ = 17638896.

The previous prime is 18721601. The next prime is 18721627. The reversal of 18721609 is 90612781.

It is a happy number.

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 18721609 - 2³ = 18721601 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18721601) 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 7 ways as a sum of consecutive naturals, for example, 4534 + ... + 7615.

It is an arithmetic number, because the mean of its divisors is an integer number (2478600).

Almost surely, 2^18721609 is an apocalyptic number.

It is an amenable number.

18721609 is a deficient number, since it is larger than the sum of its proper divisors (1107191).

18721609 is a wasteful number, since it uses less digits than its factorization.

18721609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12239.

The product of its (nonzero) digits is 6048, while the sum is 34.

The square root of 18721609 is about 4326.8474666898. The cubic root of 18721609 is about 265.5304859405.

It can be divided in two parts, 1872 and 1609, that added together give a square (3481 = 59²).

The spelling of 18721609 in words is "eighteen million, seven hundred twenty-one thousand, six hundred nine".