18997989 has 4 divisors (see below), whose sum is σ = 25330656. Its totient is φ = 12665324.

The previous prime is 18997973. The next prime is 18997991. The reversal of 18997989 is 98979981.

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, and also an emirpimes, since its reverse is a distinct semiprime: 98979981 = 3 ⋅32993327.

It is a cyclic number.

It is not a de Polignac number, because 18997989 - 2⁴ = 18997973 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18997919) 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, 3166329 + ... + 3166334.

It is an arithmetic number, because the mean of its divisors is an integer number (6332664).

Almost surely, 2^18997989 is an apocalyptic number.

It is an amenable number.

18997989 is a deficient number, since it is larger than the sum of its proper divisors (6332667).

18997989 is an equidigital number, since it uses as much as digits as its factorization.

18997989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6332666.

The product of its digits is 2939328, while the sum is 60.

The square root of 18997989 is about 4358.6682599161. The cubic root of 18997989 is about 266.8307502318.

The spelling of 18997989 in words is "eighteen million, nine hundred ninety-seven thousand, nine hundred eighty-nine".