18640991 has 4 divisors (see below), whose sum is σ = 18957000. Its totient is φ = 18324984.

The previous prime is 18640987. The next prime is 18641011. The reversal of 18640991 is 19904681.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 18640991 - 2² = 18640987 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 (18640931) 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, 157916 + ... + 158033.

It is an arithmetic number, because the mean of its divisors is an integer number (4739250).

Almost surely, 2^18640991 is an apocalyptic number.

18640991 is a deficient number, since it is larger than the sum of its proper divisors (316009).

18640991 is an equidigital number, since it uses as much as digits as its factorization.

18640991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 316008.

The product of its (nonzero) digits is 15552, while the sum is 38.

The square root of 18640991 is about 4317.5213954305. The cubic root of 18640991 is about 265.1487997831.

The spelling of 18640991 in words is "eighteen million, six hundred forty thousand, nine hundred ninety-one".