18910991 has 8 divisors (see below), whose sum is σ = 21527424. Its totient is φ = 16444120.

The previous prime is 18910981. The next prime is 18910993. The reversal of 18910991 is 19901981.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a de Polignac number, because none of the positive numbers 2^k-18910991 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 (18910993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 37121 + ... + 37626.

It is an arithmetic number, because the mean of its divisors is an integer number (2690928).

Almost surely, 2^18910991 is an apocalyptic number.

18910991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

18910991 is a deficient number, since it is larger than the sum of its proper divisors (2616433).

18910991 is a wasteful number, since it uses less digits than its factorization.

18910991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 74781.

The product of its (nonzero) digits is 5832, while the sum is 38.

The square root of 18910991 is about 4348.6769252268. The cubic root of 18910991 is about 266.4228251882.

The spelling of 18910991 in words is "eighteen million, nine hundred ten thousand, nine hundred ninety-one".