18001999 has 2 divisors, whose sum is σ = 18002000. Its totient is φ = 18001998.

The previous prime is 18001981. The next prime is 18002003. The reversal of 18001999 is 99910081.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 18001999 - 2⁷ = 18001871 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18001909) 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 as a sum of consecutive naturals, namely, 9000999 + 9001000.

It is an arithmetic number, because the mean of its divisors is an integer number (9001000).

Almost surely, 2^18001999 is an apocalyptic number.

18001999 is a deficient number, since it is larger than the sum of its proper divisors (1).

18001999 is an equidigital number, since it uses as much as digits as its factorization.

18001999 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5832, while the sum is 37.

The square root of 18001999 is about 4242.8762649882. The cubic root of 18001999 is about 262.0838406582.

It can be divided in two parts, 1 and 8001999, that added together give a triangular number (8002000 = T₄₀₀₀).

The spelling of 18001999 in words is "eighteen million, one thousand, nine hundred ninety-nine".