18506991 has 4 divisors (see below), whose sum is σ = 24675992. Its totient is φ = 12337992.

The previous prime is 18506987. The next prime is 18507011. The reversal of 18506991 is 19960581.

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

It is not a de Polignac number, because 18506991 - 2² = 18506987 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 (18506951) 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, 3084496 + ... + 3084501.

It is an arithmetic number, because the mean of its divisors is an integer number (6168998).

Almost surely, 2^18506991 is an apocalyptic number.

18506991 is a deficient number, since it is larger than the sum of its proper divisors (6169001).

18506991 is an equidigital number, since it uses as much as digits as its factorization.

18506991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6169000.

The product of its (nonzero) digits is 19440, while the sum is 39.

The square root of 18506991 is about 4301.9752440013. The cubic root of 18506991 is about 264.5119342149.

The spelling of 18506991 in words is "eighteen million, five hundred six thousand, nine hundred ninety-one".