18691987 has 8 divisors (see below), whose sum is σ = 19201536. Its totient is φ = 18188352.

The previous prime is 18691973. The next prime is 18692021. The reversal of 18691987 is 78919681.

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

It is a cyclic number.

It is not a de Polignac number, because 18691987 - 2¹⁵ = 18659219 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18691987.

It is not an unprimeable number, because it can be changed into a prime (18691927) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5343 + ... + 8119.

It is an arithmetic number, because the mean of its divisors is an integer number (2400192).

Almost surely, 2^18691987 is an apocalyptic number.

18691987 is a deficient number, since it is larger than the sum of its proper divisors (509549).

18691987 is a wasteful number, since it uses less digits than its factorization.

18691987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2957.

The product of its digits is 217728, while the sum is 49.

The square root of 18691987 is about 4323.4230651187. The cubic root of 18691987 is about 265.3903680677.

The spelling of 18691987 in words is "eighteen million, six hundred ninety-one thousand, nine hundred eighty-seven".