18664991 has 4 divisors (see below), whose sum is σ = 18874800. Its totient is φ = 18455184.

The previous prime is 18664981. The next prime is 18664993. The reversal of 18664991 is 19946681.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18664991 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18664993) 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, 104771 + ... + 104948.

It is an arithmetic number, because the mean of its divisors is an integer number (4718700).

Almost surely, 2^18664991 is an apocalyptic number.

18664991 is a deficient number, since it is larger than the sum of its proper divisors (209809).

18664991 is an equidigital number, since it uses as much as digits as its factorization.

18664991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 209808.

The product of its digits is 93312, while the sum is 44.

The square root of 18664991 is about 4320.2998738514. The cubic root of 18664991 is about 265.2625427014.

The spelling of 18664991 in words is "eighteen million, six hundred sixty-four thousand, nine hundred ninety-one".