1800021989 has 4 divisors (see below), whose sum is σ = 1800922656. Its totient is φ = 1799121324.

The previous prime is 1800021961. The next prime is 1800022069. The reversal of 1800021989 is 9891200081.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1800021989 - 2²⁸ = 1531586533 is a prime.

It is a super-2 number, since 2×1800021989² = 6480158321767032242, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1800021959) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 447329 + ... + 451334.

It is an arithmetic number, because the mean of its divisors is an integer number (450230664).

Almost surely, 2^1800021989 is an apocalyptic number.

It is an amenable number.

1800021989 is a deficient number, since it is larger than the sum of its proper divisors (900667).

1800021989 is an equidigital number, since it uses as much as digits as its factorization.

1800021989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 900666.

The product of its (nonzero) digits is 10368, while the sum is 38.

The square root of 1800021989 is about 42426.6660132516. Note that the first 3 decimals coincide. The cubic root of 1800021989 is about 1216.4453524849.

The spelling of 1800021989 in words is "one billion, eight hundred million, twenty-one thousand, nine hundred eighty-nine".