18887991 has 8 divisors (see below), whose sum is σ = 26279040. Its totient is φ = 12044472.

The previous prime is 18887987. The next prime is 18887993. The reversal of 18887991 is 19978881.

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

It is not a de Polignac number, because 18887991 - 2² = 18887987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18887993) 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, 136801 + ... + 136938.

It is an arithmetic number, because the mean of its divisors is an integer number (3284880).

Almost surely, 2^18887991 is an apocalyptic number.

18887991 is a deficient number, since it is larger than the sum of its proper divisors (7391049).

18887991 is a wasteful number, since it uses less digits than its factorization.

18887991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 273765.

The product of its digits is 290304, while the sum is 51.

The square root of 18887991 is about 4346.0316381729. The cubic root of 18887991 is about 266.3147714311.

The spelling of 18887991 in words is "eighteen million, eight hundred eighty-seven thousand, nine hundred ninety-one".