18087991 has 2 divisors, whose sum is σ = 18087992. Its totient is φ = 18087990.

The previous prime is 18087977. The next prime is 18088027. The reversal of 18087991 is 19978081.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 18087991 - 2⁷ = 18087863 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18087691) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9043995 + 9043996.

It is an arithmetic number, because the mean of its divisors is an integer number (9043996).

Almost surely, 2^18087991 is an apocalyptic number.

18087991 is a deficient number, since it is larger than the sum of its proper divisors (1).

18087991 is an equidigital number, since it uses as much as digits as its factorization.

18087991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 36288, while the sum is 43.

The square root of 18087991 is about 4252.9978838462. The cubic root of 18087991 is about 262.5004855622.

The spelling of 18087991 in words is "eighteen million, eighty-seven thousand, nine hundred ninety-one".